Release script fails with a newer git version

[dprotaso]

I'm using git version 2.33.0

Remote upstream URL is '[email protected]:dprotaso/serving.git'
+ [[ -z [email protected]:dprotaso/serving.git ]]
+ setup_branch
+ [[ -z release-1.1 ]]
+ git fetch https://github.com/dprotaso/serving release-1.1:upstream/release-1.1
fatal: Refusing to fetch into current branch refs/heads/upstream/release-1.1 of non-bare repository
+ ((  IS_PROW  ))
+ git checkout -b release-1.1 upstream/release-1.1
warning: refname 'upstream/release-1.1' is ambiguous.
warning: refname 'upstream/release-1.1' is ambiguous.
fatal: Ambiguous object name: 'upstream/release-1.1'.
+ abort 'cannot checkout branch release-1.1'
+ echo 'error: cannot checkout branch release-1.1'
error: cannot checkout branch release-1.1