Fix BulkInsert cop to also check ::Gitlab

The cop was previously not detecting when the `Gitlab` module was
accessed via the top-level namespace `::Gitlab::Database.bulk_insert`.

rubocop/cop/gitlab/bulk_insert.rb

@@ -9,7 +9,7 @@ module RuboCop
         MSG = 'Use the `BulkInsertSafe` concern, instead of using `Gitlab::Database.bulk_insert`. See https://docs.gitlab.com/ee/development/insert_into_tables_in_batches.html'
 
         def_node_matcher :raw_union?, <<~PATTERN
-          (send (const (const nil? :Gitlab) :Database) :bulk_insert ...)
+          (send (const (const _ :Gitlab) :Database) :bulk_insert ...)
         PATTERN
 
         def on_send(node)

spec/rubocop/cop/gitlab/bulk_insert_spec.rb

@@ -13,7 +13,14 @@ RSpec.describe RuboCop::Cop::Gitlab::BulkInsert, type: :rubocop do
   it 'flags the use of Gitlab::Database.bulk_insert' do
     expect_offense(<<~SOURCE)
     Gitlab::Database.bulk_insert('merge_request_diff_files', rows)
-    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use the `BulkInsertSafe` concern, instead of using `Gitlab::Database.bulk_insert`. See https://docs.gitlab.com/ee/development/insert_into_tables_in_batches.html
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ #{RuboCop::Cop::Gitlab::BulkInsert::MSG}
+    SOURCE
+  end
+
+  it 'flags the use of ::Gitlab::Database.bulk_insert' do
+    expect_offense(<<~SOURCE)
+    ::Gitlab::Database.bulk_insert('merge_request_diff_files', rows)
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ #{RuboCop::Cop::Gitlab::BulkInsert::MSG}
     SOURCE
   end
 end