Use readable texts in admin budgets test

Particularly the line with `within "tr", text: "Finished budget" do` is
now easier to read.

This way we avoid a potential pitfall. Imagine that the factory which
creates a finished budget generated a budget with the name "COMPLETED
Budget 1". Then the test:

```
within "#budget_#{finished_budget.id}" do
  expect(page).to have_content("COMPLETED")
end
```

Would pass even if we didn't add the text "COMPLETED" anywhere else,
because it would be included in the name of the budget.

spec/system/admin/budgets_spec.rb

@@ -27,36 +27,38 @@ describe "Admin budgets", :admin do
     end
 
     scenario "Filters by phase" do
-      drafting_budget  = create(:budget, :drafting)
+      create(:budget, :drafting, name: "Drafting budget")
-      accepting_budget = create(:budget, :accepting)
+      create(:budget, :accepting, name: "Accepting budget")
-      selecting_budget = create(:budget, :selecting)
+      create(:budget, :selecting, name: "Selecting budget")
-      balloting_budget = create(:budget, :balloting)
+      create(:budget, :balloting, name: "Balloting budget")
-      finished_budget  = create(:budget, :finished)
+      create(:budget, :finished, name: "Finished budget")
 
       visit admin_budgets_path
-      expect(page).to have_content(drafting_budget.name)
-      expect(page).to have_content(accepting_budget.name)
-      expect(page).to have_content(selecting_budget.name)
-      expect(page).to have_content(balloting_budget.name)
-      expect(page).to have_content(finished_budget.name)
 
-      within "#budget_#{finished_budget.id}" do
+      expect(page).to have_content "Drafting budget"
-        expect(page).to have_content("COMPLETED")
+      expect(page).to have_content "Accepting budget"
+      expect(page).to have_content "Selecting budget"
+      expect(page).to have_content "Balloting budget"
+
+      within "tr", text: "Finished budget" do
+        expect(page).to have_content "COMPLETED"
       end
 
       click_link "Finished"
-      expect(page).not_to have_content(drafting_budget.name)
+
-      expect(page).not_to have_content(accepting_budget.name)
+      expect(page).not_to have_content "Drafting budget"
-      expect(page).not_to have_content(selecting_budget.name)
+      expect(page).not_to have_content "Accepting budget"
-      expect(page).not_to have_content(balloting_budget.name)
+      expect(page).not_to have_content "Selecting budget"
-      expect(page).to have_content(finished_budget.name)
+      expect(page).not_to have_content "Balloting budget"
+      expect(page).to have_content "Finished budget"
 
       click_link "Open"
-      expect(page).to have_content(drafting_budget.name)
+
-      expect(page).to have_content(accepting_budget.name)
+      expect(page).to have_content "Drafting budget"
-      expect(page).to have_content(selecting_budget.name)
+      expect(page).to have_content "Accepting budget"
-      expect(page).to have_content(balloting_budget.name)
+      expect(page).to have_content "Selecting budget"
-      expect(page).not_to have_content(finished_budget.name)
+      expect(page).to have_content "Balloting budget"
+      expect(page).not_to have_content "Finished budget"
     end
 
     scenario "Filters are properly highlighted" do