Apply Rails/SaveBang rubocop rule

Having exceptions is better than having silent bugs.

There are a few methods I've kept the same way they were.

The `RelatedContentScore#score_with_opposite` method is a bit peculiar:
it creates scores for both itself and the opposite related content,
which means the opposite related content will try to create the same
scores as well.

We've already got a test to check `Budget::Ballot#add_investment` when
creating a line fails ("Edge case voting a non-elegible investment").

Finally, the method `User#send_oauth_confirmation_instructions` doesn't
update the record when the email address isn't already present, leading
to the test "Try to register with the email of an already existing user,
when an unconfirmed email was provided by oauth" fo fail if we raise an
exception for an invalid user. That's because updating a user's email
doesn't update the database automatically, but instead a confirmation
email is sent.

There are also a few false positives for classes which don't have bang
methods (like the GraphQL classes) or destroying attachments.

For these reasons, I'm adding the rule with a "Refactor" severity,
meaning it's a rule we can break if necessary.

spec/features/admin/budget_investments_spec.rb

@@ -105,7 +105,7 @@ describe "Admin budget investments" do
         expect(page).to have_content("Health")
       end
 
-      budget_investment3.update(administrator_id: admin.id)
+      budget_investment3.update!(administrator_id: admin.id)
       visit admin_budget_budget_investments_path(budget_id: budget.id)
 
       within("#budget_investment_#{budget_investment3.id}") do
@@ -518,8 +518,8 @@ describe "Admin budget investments" do
       investment1.set_tag_list_on(:valuation, "Teachers")
       investment2.set_tag_list_on(:valuation, "Hospitals")
 
-      investment1.save
-      investment2.save
+      investment1.save!
+      investment2.save!
 
       visit admin_budget_budget_investments_path(budget_id: budget.id)
 
@@ -534,8 +534,8 @@ describe "Admin budget investments" do
       investment1.set_tag_list_on(:valuation, "Roads")
       investment2.set_tag_list_on(:valuation, "Accessibility")
 
-      investment1.save
-      investment2.save
+      investment1.save!
+      investment2.save!
 
       visit admin_budget_budget_investments_path(budget_id: budget.id)
 
@@ -544,7 +544,7 @@ describe "Admin budget investments" do
     end
 
     scenario "Disable 'Calculate winner' button if incorrect phase" do
-      budget.update(phase: "reviewing_ballots")
+      budget.update!(phase: "reviewing_ballots")
 
       visit admin_budget_budget_investments_path(budget)
 
@@ -558,7 +558,7 @@ describe "Admin budget investments" do
 
       expect(page).to have_link "Calculate Winner Investments"
 
-      budget.update(phase: "accepting")
+      budget.update!(phase: "accepting")
 
       visit admin_budget_budget_investments_path(budget)
 
@@ -1202,7 +1202,7 @@ describe "Admin budget investments" do
     scenario "Adds existing valuation tags", :js do
       budget_investment1 = create(:budget_investment)
       budget_investment1.set_tag_list_on(:valuation, "Education, Health")
-      budget_investment1.save
+      budget_investment1.save!
 
       budget_investment2 = create(:budget_investment)
 
@@ -1240,7 +1240,7 @@ describe "Admin budget investments" do
     scenario "Changes valuation and user generated tags" do
       budget_investment = create(:budget_investment, tag_list: "Park")
       budget_investment.set_tag_list_on(:valuation, "Education")
-      budget_investment.save
+      budget_investment.save!
 
       visit admin_budget_budget_investment_path(budget_investment.budget, budget_investment)
 
@@ -1480,7 +1480,7 @@ describe "Admin budget investments" do
     end
 
     scenario "Show only selected text when budget is finished" do
-      budget.update(phase: "finished")
+      budget.update!(phase: "finished")
 
       visit admin_budget_budget_investments_path(budget)
 
@@ -1582,8 +1582,8 @@ describe "Admin budget investments" do
     scenario "Mark as visible to valuator", :js do
       investment1.valuators << valuator
       investment2.valuators << valuator
-      investment1.update(administrator: admin)
-      investment2.update(administrator: admin)
+      investment1.update!(administrator: admin)
+      investment2.update!(administrator: admin)
 
       visit admin_budget_budget_investments_path(budget)
       click_link "Advanced filters"
@@ -1605,13 +1605,13 @@ describe "Admin budget investments" do
     end
 
     scenario "Shows the correct investments to valuators" do
-      investment1.update(visible_to_valuators: true)
-      investment2.update(visible_to_valuators: false)
+      investment1.update!(visible_to_valuators: true)
+      investment2.update!(visible_to_valuators: false)
 
       investment1.valuators << valuator
       investment2.valuators << valuator
-      investment1.update(administrator: admin)
-      investment2.update(administrator: admin)
+      investment1.update!(administrator: admin)
+      investment2.update!(administrator: admin)
 
       login_as(valuator.user.reload)
       visit root_path
@@ -1627,12 +1627,12 @@ describe "Admin budget investments" do
     end
 
     scenario "Unmark as visible to valuator", :js do
-      budget.update(phase: "valuating")
+      budget.update!(phase: "valuating")
 
       investment1.valuators << valuator
       investment2.valuators << valuator
-      investment1.update(administrator: admin, visible_to_valuators: true)
-      investment2.update(administrator: admin, visible_to_valuators: true)
+      investment1.update!(administrator: admin, visible_to_valuators: true)
+      investment2.update!(administrator: admin, visible_to_valuators: true)
 
       visit admin_budget_budget_investments_path(budget)
 
@@ -1682,7 +1682,7 @@ describe "Admin budget investments" do
 
     scenario "Keeps the valuation tags", :js do
       investment1.set_tag_list_on(:valuation, %w[Possimpible Truthiness])
-      investment1.save
+      investment1.save!
 
       visit admin_budget_budget_investments_path(budget)