Restore original index error check for snippet commit check

The Rugged implementation of the `UserCommitFiles` RPC raised a
`Gitlab::Git::Index::IndexError` when an invalid file was written
(e.g. `.git/hooks/pre-commit`), but the Go implementation previously
swallowed the Git2Go equivalent error and raised a
`Gitlab::Git::CommandError` instead.

Now that https://gitlab.com/gitlab-org/gitaly/-/merge_requests/3165 has
been merged, we partially revert the change in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/54662 to check the
original error type.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/322096

app/models/snippet_repository.rb

@@ -115,10 +115,8 @@ class SnippetRepository < ApplicationRecord
   end
 
   def invalid_path_error?(err)
-    (err.is_a?(Gitlab::Git::Index::IndexError) &&
-      err.message.downcase.start_with?('invalid path', 'path cannot include directory traversal')) ||
-    (err.is_a?(Gitlab::Git::CommandError) &&
-      err.message.include?('CreateFile: invalid path'))
+    err.is_a?(Gitlab::Git::Index::IndexError) &&
+      err.message.downcase.start_with?('invalid path', 'path cannot include directory traversal')
   end
 
   def invalid_signature_error?(err)

changelogs/unreleased/322096-fj-fix-regression-in-snippet-background-migration.yml

----
-title: Fix snippet commit bug because of different Gitaly error
-merge_request: 54662
-author:
-type: fixed