Update GitHub actions

[ArBridgeman]

Summary

• ✅ checkout to v6
• ✅ upload-pages-artifact to v4 -> need to verify post merge that works as expected
• ✅ download-artifact from 6 to 7
• ✅ upload-artifact from 5 to 6

Discussion

upload-pages-artifact to v4

From v3 to v4, the upload-pages-artifact stopped uploading dotfiles. Currently, our documentation is put into a folder called .html-documentation. v4 was released 2025-Aug, and it seems like the developers plan to mostly stick by this decision:

• ignore all hidden files when creating zip actions/upload-pages-artifact#102

Obviously, some groups need dotfiles to be uploaded, so there is an ongoing effort to have them consciously re-added:

• Allow publishing of hidden/dot-prefixed files again actions/upload-pages-artifact#129

In checking the PTB's documentation for .dotfiles, we arrive at:

❯ ls -a .hmtl-documentation/ | grep "^\."
.
..
.buildinfo
.doctrees

In our gh-pages.yml, we were already manually removing .doctrees and we do not need the .buildinfo uploaded. So it seems like that as long as we move .html-documentation to html-documentation that it would work as desired:

1. just convert in the gh-pages.yml - easy
2. change all cases of .html-documentation to html-documentation - more difficult as need to update docs:build, .gitignore, and cookiecutter template too. Downstream projects would also need to modify their .gitignores to prevent accidentally committing documentation files.