Enable frozen string for most of spec/lib

spec/lib/gitlab/**/* will be covered in
subsequent MR's, but at least we can
lint the rest of the directory.

Partially addresses:

https://gitlab.com/gitlab-org/gitlab/issues/27703

.rubocop.yml

@@ -56,7 +56,7 @@ Style/FrozenStringLiteralComment:
     - 'qa/**/*'
     - 'rubocop/**/*'
     - 'scripts/**/*'
-    - 'spec/lib/**/*'
+    - 'spec/lib/gitlab/**/*'
 
 RSpec/FilePath:
   Exclude:

spec/lib/banzai/filter/asset_proxy_filter_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Banzai::Filter::AssetProxyFilter do

spec/lib/omni_auth/strategies/saml_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe OmniAuth::Strategies::SAML, type: :strategy do