Summary

Fixes checking if a commit is signed to work when it is signed with an ssh key.

Details

• If a commit is signed with an ssh key, git needs the gpg.ssh.allowedSignersFile to be configured otherwise it will output an error message.
• this configures it with an empty file to successfully output the commit signature status
• the CI step is to check if a commit is signed at all (status != N (not signed)), not to verify the signature (github will do that), so we just need an empty file and the ssh-signed commit's status will be U (unknown validity)