Upgrade Gitaly Gem to v13.12.0-rc1

Gitaly has extended the FindRemoteRootRefs RPC to accept a URL instead
of a remote name, so we need to upgrade the Gitaly Gem hosting protobuf
declarations to start using it.

Gemfile

@@ -481,7 +481,7 @@ end
 gem 'spamcheck', '~> 0.0.5'
 
 # Gitaly GRPC protocol definitions
-gem 'gitaly', '~> 13.11.0.pre.rc1'
+gem 'gitaly', '~> 13.12.0.pre.rc1'
 
 gem 'grpc', '~> 1.30.2'
 

Gemfile.lock

@@ -439,7 +439,7 @@ GEM
       rails (>= 3.2.0)
     git (1.7.0)
       rchardet (~> 1.8)
-    gitaly (13.11.0.pre.rc1)
+    gitaly (13.12.0.pre.rc1)
       grpc (~> 1.0)
     github-markup (1.7.0)
     gitlab (4.16.1)
@@ -1446,7 +1446,7 @@ DEPENDENCIES
   gettext (~> 3.3)
   gettext_i18n_rails (~> 1.8.0)
   gettext_i18n_rails_js (~> 1.3)
-  gitaly (~> 13.11.0.pre.rc1)
+  gitaly (~> 13.12.0.pre.rc1)
   github-markup (~> 1.7.0)
   gitlab-chronic (~> 0.10.5)
   gitlab-dangerfiles (~> 2.0.0)