I am facing a similar problem. The issue lies where the github:repo:push
action uses a helper that initializes a git repo, https://github.com/backstage/backstage/blob/master/plugins/scaffolder-backend-module-github/src/actions/github.ts#L275, and uses this helper function here: https://github.com/backstage/backstage/blob/master/plugins/scaffolder-node/src/actions/gitHelpers.ts#L49-L52
My suggestion is to follow the GitHub issue https://github.com/backstage/backstage/issues/28749 to allow an action like: github:branch:push
.