Enable Lint/StringConversionInInterpolation cop and autocorrect offenses

.rubocop.yml

.rubocop_todo.yml

app/controllers/concerns/spammable_actions.rb

app/helpers/projects_helper.rb

app/models/commit_range.rb

app/services/system_hooks_service.rb

app/services/system_note_service.rb

spec/finders/access_requests_finder_spec.rb

.../lib/gitlab/import_export/attribute_configuration_spec.rb

spec/services/members/approve_access_request_service_spec.rb

spec/services/members/request_access_service_spec.rb