[GHF] Fix regression
Introduced by https://github.com/pytorch/pytorch/pull/103679
That was not covered by tests :(
Discovered while looking at https://github.com/pytorch/pytorch/actions/runs/5281833681/jobs/9555936751#step:5:24
Locally tested by running `python -c "from trymerge import gh_get_pr_info;print(gh_get_pr_info('pytorch', 'pytorch', 103685)['author'])"`
