Merge branch 'frozen-string-enable-lib-gitlab-gpg' into 'master'

Enable frozen string for spec/lib/gitlab/gpg

See merge request gitlab-org/gitlab!20502

spec/lib/gitlab/gpg/commit_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Gpg::Commit do

spec/lib/gitlab/gpg/invalid_gpg_signature_updater_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 RSpec.describe Gitlab::Gpg::InvalidGpgSignatureUpdater do