Collect after del in tests, add python 3.13 to non-dev CI

[braingram]

Description

This PR adds python 3.13 testing to our regular (non-devdeps) CI and adds gc.collect(2) calls after del calls in our tests.

I'm not certain the issue but my suspicion is that the python 3.13 changes to the garbage collector means that some of our tests that rely on implicit garbage collection may now intermittently fail with python 3.13. These tests often make an object, add it's reference in some way to asdf (which should grab a weakref for these tests), then del the object and check that asdf correctly handles the failure to resolve the weakref. If garbage collection doesn't occur between the del and the assert testing the weakref the test will fail. Hopefully adding explicit calls to gc.collect will fix the issue.

It looks like with python 3.13 gc.collect is equivalent to gc.collect(2). This is different compared to python 3.12 and the updates here use gc.collect(2) to try to have similar behavior for python 3.13 and older versions.

Closes #1834

Checklist:

• pre-commit checks ran successfully

• tests ran successfully

• for a public change, added a towncrier news fragment

  changes/<PR#>.<changetype>.rst

  • changes/<PR#>.feature.rst: new feature
  • changes/<PR#>.bugfix.rst: bug fix
  • changes/<PR#>.doc.rst: documentation change
  • changes/<PR#>.removal.rst: deprecation or removal of public API
  • changes/<PR#>.general.rst: infrastructure or miscellaneous change

• for a public change, updated documentation

• for any new features, unit tests were added

[zacharyburnett]

no idea how the garbage collector works (do you just tell it to collect and it frees the memory?) but this LGTM

EDIT: oh I didn't read the description first, that makes sense

[braingram]

Thanks for the review!

Here's a decent looking resource: https://stackify.com/python-garbage-collection/
and one that goes into low level details: https://devguide.python.org/internals/garbage-collector/index.html#garbage-collector-design

I opened a test PR to see if I could replicate the reported issue in our CI with no luck: #1836
I'm doing some local tests now (to try and reproduce the reported issue). If it's ok with you I'll leave this PR unmerged until I finish the local tests.

[braingram]

Nice! I was able to replicate this with a dev install of python 3.13 (rc2+) and running the failing test in isolation. If I then add the gc.collect the test passes.