Update gitlab-styles to 5.1.0

.rubocop_todo.yml

Gemfile

Gemfile.lock

...ec/lib/analytics/merge_request_metrics_calculator_spec.rb

ee/spec/lib/gitlab/audit/events/preloader_spec.rb

ee/spec/lib/gitlab/checks/matching_merge_request_spec.rb

ee/spec/models/audit_event_spec.rb

ee/spec/models/ci/daily_build_group_report_result_spec.rb

ee/spec/models/ee/vulnerability_spec.rb

ee/spec/models/vulnerabilities/finding_spec.rb

ee/spec/requests/api/analytics/code_review_analytics_spec.rb

...pec/requests/api/graphql/vulnerabilities/location_spec.rb

ee/spec/requests/api/issues_spec.rb

ee/spec/services/historical_user_data/csv_service_spec.rb

rubocop/cop/line_break_around_conditional_block.rb

spec/controllers/concerns/metrics_dashboard_spec.rb

spec/features/groups/milestone_spec.rb

spec/finders/merge_requests/by_approvals_finder_spec.rb

...raphql/resolvers/merge_request_pipelines_resolver_spec.rb

spec/helpers/markup_helper_spec.rb