Describe the bug

Trying to create a pull request with gh fails if the branch given with -H does not exist locally and has the appropriate content.

Steps to reproduce the behavior

• create a commit on a local branch based on <base branch>
• push this commit to a <new remote branch>
• gh pr create -B <base branch> --fill -H <new remote branch>

Expected vs actual behavior

The pull request should be created. The problems seems to be origin/landscape/prod...landscape/prod-upgrade-2992887. This only works if the given remote branch is identical to a local branch with the same name, that has been used to create the commits. But this must not necessarily be the case.

Logs

$ gh --version
gh version 2.5.2 (2022-03-01)
https://github.com/cli/cli/releases/tag/v2.5.2

$ gh pr create  -B landscape/prod --fill  -H landscape/prod-upgrade-2992887
could not compute title or body defaults: fatal: ambiguous argument 'origin/landscape/prod...landscape/prod-upgrade-2992887': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
/usr/bin/git: exit status 128

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