Error: fatal: A branch named 'master' already exists

[glenn-jocher]

Hi, thanks for this great action! I installed in our repo and ran into an error the first time I tried to use it on this PR ultralytics/yolov5#395

A user is trying to submit a PR from their forked branch master to origin/master:

wants to merge 12 commits into ultralytics:master from topiaruss:master

fatal: A branch named 'master' already exists.

[Koenkk]

Same issue here (https://github.com/Koenkk/zigbee2mqtt/runs/984238831?check_suite_focus=true)