Fix milestones migration not updating ID sequence

When we insert a record in PostgreSQL and we specify the ID, the
internal ID sequence for that table isn't updated.

In order to keep the original IDs so we didn't break any foreign keys,
we specified the IDs when copying the table, resulting in a table having
its ID sequence with a value of an existing record. When trying to
insert a new record, we got a `PG::UniqueViolation` exception.

Updating the sequence after the data migration might not be the most
elegant solution, but it's easy to do and it's already been tested on a
production environment.

lib/tasks/migrate_milestones_and_statuses.rake

@@ -91,6 +91,10 @@ namespace :milestones do
         "budget_investment_statuses"               => "milestone_statuses",
         "budget_investment_milestone_translations" => "milestone_translations"
       }.each do |original_table, migrated_table|
+        ActiveRecord::Base.connection.execute(
+          "select setval('#{migrated_table}_id_seq', (select max(id) from #{migrated_table}));"
+        )
+
         unless count_rows(original_table) == count_rows(migrated_table)
           raise "Number of rows of old and new tables do not match! Rolling back transaction..."
         end

spec/lib/tasks/milestones_spec.rb

@@ -66,6 +66,11 @@ describe "Milestones tasks" do
       expect(milestone.updated_at.to_date).to eq Date.today
     end
 
+    it "Updates the primary key sequence correctly" do
+      run_rake_task
+      expect { create(:milestone) }.not_to raise_exception
+    end
+
     context "Milestone has images and documents" do
       let(:milestone_id) do
         ActiveRecord::Base.connection.execute(