Move git calls for `Repository#update_branch` inside Gitlab::Git

This prepares this code for migration to Gitaly.

ee/app/models/ee/repository.rb

@@ -35,12 +35,5 @@ module EE
       # Gitaly migration: https://gitlab.com/gitlab-org/gitaly/issues/1243
       ::Gitlab::GitalyClient::StorageSettings.allow_disk_access { super }
     end
-
-    # Gitaly migration: https://gitlab.com/gitlab-org/gitaly/issues/1246
-    def update_branch(user, branch_name, newrev, oldrev)
-      ::Gitlab::GitalyClient::StorageSettings.allow_disk_access do
-        ::Gitlab::Git::OperationService.new(user, raw_repository).update_branch(branch_name, newrev, oldrev)
-      end
-    end
   end
 end

ee/app/services/projects/update_mirror_service.rb

@@ -97,7 +97,10 @@ module Projects
         newrev = upstream.dereferenced_target.sha
         oldrev = local.dereferenced_target.sha
 
-        repository.update_branch(current_user, branch_name, newrev, oldrev)
+        # Gitaly migration: https://gitlab.com/gitlab-org/gitaly/issues/1246
+        ::Gitlab::GitalyClient::StorageSettings.allow_disk_access do
+          repository.update_branch(branch_name, user: current_user, newrev: newrev, oldrev: oldrev)
+        end
       elsif branch_name == project.default_branch
         # Cannot be updated
         errors << "The default branch (#{project.default_branch}) has diverged from its upstream counterpart and could not be updated automatically."

lib/gitlab/git/repository.rb

@@ -699,6 +699,10 @@ module Gitlab
         end
       end
 
+      def update_branch(branch_name, user:, newrev:, oldrev:)
+        OperationService.new(user, self).update_branch(branch_name, newrev, oldrev)
+      end
+
       def rm_branch(branch_name, user:)
         gitaly_migrate(:operation_user_delete_branch, status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |is_enabled|
           if is_enabled
@@ -2004,8 +2008,7 @@ module Gitlab
 
           rebase_sha = run_git!(%w(rev-parse HEAD), chdir: rebase_path, env: env).strip
 
-          Gitlab::Git::OperationService.new(user, self)
-            .update_branch(branch, rebase_sha, branch_sha)
+          update_branch(branch, user: user, newrev: rebase_sha, oldrev: branch_sha)
 
           rebase_sha
         end