push to GAR action writes files to the repository's working directory

[mem]

Back in April it was reported that one of the shared workflows was writing stuff to the working directory while running. This PR was mentioned in that conversation.

It was then reported that push to GAR was creating a shared-workflows directory.

Now it's writing a different directory:

#16 [linux/amd64->arm64 buildtools 4/5] RUN git status && git clean -dxn
#16 0.081 HEAD detached at pull/714/merge
#16 0.081 Untracked files:
#16 0.081   (use "git add <file>..." to include in what will be committed)
#16 0.081 	_shared-workflows-push-to-gar/
#16 0.081 
#16 0.081 nothing added to commit but untracked files present (use "git add" to track)
#16 DONE 0.1s

It's creating a _shared-workflows-push-to-gar/ directory.