Add rm -f db/structure.sql to reset the test database

When `db/structure.sql` exists, it's used when doing `rails db:migrate`
instead of running the migrations. When switching to a branch with less
migrations, the test database will be created with the
`db/structure.sql` file which contains the migrations of the previous
branch. They should not be there.

To have the correct database structure for tests, the `db/structure.sql`
file must be removed before running `db:migrate`.

script/github_pr_errors

@@ -672,7 +672,7 @@ class Formatter
   end
 
   def reset_test_database_command
-    "bin/rails db:drop db:create db:migrate RAILS_ENV=test"
+    "rm -f db/structure.sql; bin/rails db:drop db:create db:migrate RAILS_ENV=test"
   end
 
   def precompile_assets_command