Assign Backend reviewers too for most of Database related files

This makes this clearer for contributors to request review from Backend
reviewers, and Backend maintainers for these files as well, as app and
lib directories affect the Rails application

spec/tooling/danger/project_helper_spec.rb

@@ -139,18 +139,18 @@ RSpec.describe Tooling::Danger::ProjectHelper do
       'db/post_migrate/foo'                                       | [:database, :migration]
       'ee/db/geo/migrate/foo'                                     | [:database, :migration]
       'ee/db/geo/post_migrate/foo'                                | [:database, :migration]
-      'app/models/project_authorization.rb'                       | [:database]
-      'app/services/users/refresh_authorized_projects_service.rb' | [:database]
-      'app/services/authorized_project_update/find_records_due_for_refresh_service.rb' | [:database]
-      'lib/gitlab/background_migration.rb'                        | [:database]
-      'lib/gitlab/background_migration/foo'                       | [:database]
-      'ee/lib/gitlab/background_migration/foo'                    | [:database]
-      'lib/gitlab/database.rb'                                    | [:database]
-      'lib/gitlab/database/foo'                                   | [:database]
-      'ee/lib/gitlab/database/foo'                                | [:database]
-      'lib/gitlab/github_import.rb'                               | [:database]
-      'lib/gitlab/github_import/foo'                              | [:database]
-      'lib/gitlab/sql/foo'                                        | [:database]
+      'app/models/project_authorization.rb'                       | [:database, :backend]
+      'app/services/users/refresh_authorized_projects_service.rb' | [:database, :backend]
+      'app/services/authorized_project_update/find_records_due_for_refresh_service.rb' | [:database, :backend]
+      'lib/gitlab/background_migration.rb'                        | [:database, :backend]
+      'lib/gitlab/background_migration/foo'                       | [:database, :backend]
+      'ee/lib/gitlab/background_migration/foo'                    | [:database, :backend]
+      'lib/gitlab/database.rb'                                    | [:database, :backend]
+      'lib/gitlab/database/foo'                                   | [:database, :backend]
+      'ee/lib/gitlab/database/foo'                                | [:database, :backend]
+      'lib/gitlab/github_import.rb'                               | [:database, :backend]
+      'lib/gitlab/github_import/foo'                              | [:database, :backend]
+      'lib/gitlab/sql/foo'                                        | [:database, :backend]
       'rubocop/cop/migration/foo'                                 | [:database]
 
       'db/fixtures/foo.rb'                                 | [:backend]

tooling/danger/project_helper.rb

@@ -76,11 +76,11 @@ module Tooling
         )\z}x => %i[frontend engineering_productivity],
 
         %r{\A(ee/)?db/(geo/)?(migrate|post_migrate)/} => [:database, :migration],
-        %r{\A(ee/)?db/(?!fixtures)[^/]+} => :database,
-        %r{\A(ee/)?lib/gitlab/(database|background_migration|sql|github_import)(/|\.rb)} => :database,
-        %r{\A(app/services/authorized_project_update/find_records_due_for_refresh_service)(/|\.rb)} => :database,
-        %r{\A(app/models/project_authorization|app/services/users/refresh_authorized_projects_service)(/|\.rb)} => :database,
-        %r{\A(ee/)?app/finders/} => :database,
+        %r{\A(ee/)?db/(?!fixtures)[^/]+} => [:database],
+        %r{\A(ee/)?lib/gitlab/(database|background_migration|sql|github_import)(/|\.rb)} => [:database, :backend],
+        %r{\A(app/services/authorized_project_update/find_records_due_for_refresh_service)(/|\.rb)} => [:database, :backend],
+        %r{\A(app/models/project_authorization|app/services/users/refresh_authorized_projects_service)(/|\.rb)} => [:database, :backend],
+        %r{\A(ee/)?app/finders/} => [:database, :backend],
         %r{\Arubocop/cop/migration(/|\.rb)} => :database,
 
         %r{\A(\.gitlab-ci\.yml\z|\.gitlab\/ci)} => :engineering_productivity,