DRY up conditions for files require DB review

Stop using two separate lists for the conditions which files require a
database review.

Related discussion:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30156#note_187732053

danger/database/Dangerfile

 # frozen_string_literal: true
 
-# All the files/directories that should be reviewed by the DB team.
-DB_FILES = [
-  'db/',
-  'app/models/project_authorization.rb',
-  'app/services/users/refresh_authorized_projects_service.rb',
-  'lib/gitlab/background_migration.rb',
-  'lib/gitlab/background_migration/',
-  'lib/gitlab/database.rb',
-  'lib/gitlab/database/',
-  'lib/gitlab/github_import.rb',
-  'lib/gitlab/github_import/',
-  'lib/gitlab/sql/',
-  'rubocop/cop/migration',
-  'ee/lib/gitlab/database/'
-].freeze
-
 SCHEMA_NOT_UPDATED_MESSAGE = <<~MSG
 **New %<migrations>s added but %<schema>s wasn't updated.**
 
@@ -24,20 +8,6 @@ updated too (unless the migration isn't changing the DB schema
 and isn't the most recent one).
 MSG
 
-def database_paths_requiring_review(files)
-  to_review = []
-
-  files.each do |file|
-    review = DB_FILES.any? do |pattern|
-      file.start_with?(pattern)
-    end
-
-    to_review << file if review
-  end
-
-  to_review
-end
-
 non_geo_db_schema_updated = !git.modified_files.grep(%r{\Adb/schema\.rb}).empty?
 geo_db_schema_updated = !git.modified_files.grep(%r{\Aee/db/geo/schema\.rb}).empty?
 
@@ -52,7 +22,7 @@ if geo_migration_created && !geo_db_schema_updated
   warn format(SCHEMA_NOT_UPDATED_MESSAGE, migrations: 'Geo migrations', schema: gitlab.html_link("ee/db/geo/schema.rb"))
 end
 
-db_paths_to_review = database_paths_requiring_review(helper.all_changed_files)
+db_paths_to_review = helper.changes_by_category[:database]
 
 unless db_paths_to_review.empty?
   message 'This merge request adds or changes files that require a ' \

lib/gitlab/danger/helper.rb

@@ -103,6 +103,11 @@ module Gitlab
           yarn\.lock
         )\z}x => :frontend,
 
+        %r{\A(ee/)?db/} => :database,
+        %r{\A(ee/)?lib/gitlab/(database|background_migration|sql|github_import)(/|\.rb)} => :database,
+        %r{\A(app/models/project_authorization|app/services/users/refresh_authorized_projects_service)(/|\.rb)} => :database,
+        %r{\Arubocop/cop/migration(/|\.rb)} => :database,
+
         %r{\A(ee/)?app/(?!assets|views)[^/]+} => :backend,
         %r{\A(ee/)?(bin|config|danger|generator_templates|lib|rubocop|scripts)/} => :backend,
         %r{\A(ee/)?spec/features/} => :test,
@@ -112,7 +117,6 @@ module Gitlab
         %r{\A(Dangerfile|Gemfile|Gemfile.lock|Procfile|Rakefile|\.gitlab-ci\.yml)\z} => :backend,
         %r{\A[A-Z_]+_VERSION\z} => :backend,
 
-        %r{\A(ee/)?db/} => :database,
         %r{\A(ee/)?qa/} => :qa,
 
         # Files that don't fit into any category are marked with :none

spec/lib/gitlab/danger/helper_spec.rb

@@ -87,13 +87,13 @@ describe Gitlab::Danger::Helper do
 
   describe '#changes_by_category' do
     it 'categorizes changed files' do
-      expect(fake_git).to receive(:added_files) { %w[foo foo.md foo.rb foo.js db/foo qa/foo ee/changelogs/foo.yml] }
+      expect(fake_git).to receive(:added_files) { %w[foo foo.md foo.rb foo.js db/foo lib/gitlab/database/foo.rb qa/foo ee/changelogs/foo.yml] }
       allow(fake_git).to receive(:modified_files) { [] }
       allow(fake_git).to receive(:renamed_files) { [] }
 
       expect(helper.changes_by_category).to eq(
         backend: %w[foo.rb],
-        database: %w[db/foo],
+        database: %w[db/foo lib/gitlab/database/foo.rb],
         frontend: %w[foo.js],
         none: %w[ee/changelogs/foo.yml foo.md],
         qa: %w[qa/foo],
@@ -159,9 +159,22 @@ describe Gitlab::Danger::Helper do
 
       'ee/FOO_VERSION' | :unknown
 
-      'db/foo' | :database
-      'qa/foo' | :qa
+      'db/foo'                                                    | :database
+      'ee/db/foo'                                                 | :database
+      'app/models/project_authorization.rb'                       | :database
+      'app/services/users/refresh_authorized_projects_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
+      'rubocop/cop/migration/foo'                                 | :database
 
+      'qa/foo' | :qa
       'ee/qa/foo' | :qa
 
       'changelogs/foo'    | :none