git: Fix removal of nonexistent repositories

Gitaly has changed semantics of the RemoveRepository RPC call to return
an error in case the repository that is about to be deleted doesn't
exist anymore in commit f328e3f70 (repository: Implement atomic locking
semantics for RemoveRepository, 2021-11-30). This change was required
such that Gitaly can provide proper locking semantics for repositories,
but it has broken expectations on our side that removing a nonexisting
repository is an idempotent action.

Adapt to the semantic change by rescuing from `NoRepository` errors in
`Repository#remove`.

lib/gitlab/git/repository.rb

@@ -160,6 +160,8 @@ module Gitlab
         wrapped_gitaly_errors do
           gitaly_repository_client.remove
         end
+      rescue NoRepository
+        nil
       end
 
       def replicate(source_repository)