Add postgresql 15/16 to testing matrix

Seems simple enough, thanks for keeping up with test versions!

Committed/pushed to 11.x, thanks!

We'd need a 10.1.x-specific backport patch to add there, but also thinking we can just keep these environments for 11.x/10.2.x for now.

Wondering a bit about on-commit vs. daily but can tweak that later if on-commit is too much, if anything we might want to move postgresql 12 down to daily instead.

andypost → closed merge request !4805

Automatically closed - issue fixed for 2 weeks with no activity.