Bug when jj undo-ing jj git fetch --branch

[ilyagr]

Since #1146, there is a known bug when executing jj undo after jj git fetch --branch. Subsequent jj git fetch -branch-es might pull more branches than expected.

The issue likely stems from the fact that jj undo does not undo the fetch inside the git repo. This might be related to #922 (even though this bug has nothing to do with colocated repos).

For more details, see test_git_fetch_undo in tests/test_git_fetch.rs or search for this bug's number in that file.