Fix frozen string errors in specs

ee/spec/lib/ee/gitlab/auth/ldap/sync/proxy_spec.rb

@@ -28,7 +28,7 @@ describe EE::Gitlab::Auth::LDAP::Sync::Proxy do
     end
 
     context 'with a valid LDAP group that contains ASCII-8BIT-encoded Unicode data' do
-      let(:username) { 'Méräy'.force_encoding('ASCII-8BIT') }
+      let(:username) { (+'Méräy').force_encoding('ASCII-8BIT') }
       let(:dns) { [user_dn(username)] }
 
       it 'return members DNs' do

ee/spec/lib/gitlab/auth/o_auth/auth_hash_spec.rb

@@ -38,6 +38,6 @@ describe Gitlab::Auth::OAuth::AuthHash do
   end
 
   def ascii(text)
-    text.force_encoding(Encoding::ASCII_8BIT)
+    text.dup.force_encoding(Encoding::ASCII_8BIT)
   end
 end