Couldn't create new Git branch. Unable to create branch 'tmp_spectacles_b26dbc2d02

[DM218]

Error seen: Couldn't create new Git branch. Unable to create branch 'tmp_spectacles_b26dbc2d02' in project 'xxx'. Confirm the branch doesn't already exist and try again.

Run in verbose mode (-v) or check your log file to see the full response from the Looker API. For support, please create an issue at https://github.com/spectacles-ci/spectacles/issues

.. Spectacles received a 422 response code from the Looker API with the following
details: {
"message": "error: src refspec tmp_spectacles_b26dbc2d02 does not
match any\nerror: failed to push some refs to 'github.com:sky-uk/looker-
poc.git'\n",
"documentation_url": "https://cloud.google.com/looker/docs/r/err/4.0
/422/post/projects/:project_id/git_branch"
}

[advincze-nelly]

i had a similar issue running on github actions pull requests:
using

--commit-ref ${{ github.event.pull_request.head.sha }} 

instead of

--commit-ref ${{ github.sha }} 

fixed it for me