fix(commit fixup): handle autostashing dirty changes #868
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If there are unstaged changes in the worktree when using commit fixup
to fix up a downstack branch, we should not pop the autostashed changes
until after the upstack restack is complete,
and we've switched back to the original branch (not the fixed branch).
Ref: #867 (comment)
[skip changelog]: New entry not required as fixup hasn't been released yet.