MAINT: Upload nightly wheels and run packaging on PRs and pushes

[larsoner]

It seems like it should be okay to run packaging steps on each PR and push to main, but we'll see if it adds a lot of overhead. Then also add a nightly wheel upload to https://anaconda.org/scientific-python-nightly-wheels.

This will require getting an Anaconda token from the appropriate folks and adding it as a secret, so marking as a draft for now.

[larsoner]

Argh it creates a second set of duplicate tests so that's no good. So we should remove the pull_request: before merging, too. I'll leave it in for now just so that we can see things green first.

[larsoner]

Okay this looks pretty reasonable, I think it maybe would have worked:

https://github.com/pydata/pydata-sphinx-theme/actions/runs/9389922668/job/25859082226

I'll disable the PR build part and then work on the token!

[larsoner]

Yep that's right

[trallard]

This looks good, so will go ahead and merge 🚀