Fix reference docs test in testing suite
The purpose of this MR is to grab the igwn release of PESummary from the igwn-py310.yaml rather than igwn-py39.yaml since the latter no longer exists.
The purpose of this MR is to grab the igwn release of PESummary from the igwn-py310.yaml rather than igwn-py39.yaml since the latter no longer exists.