6.x backports

[ianthomas23]

Backports from main to 6.x branch, in preparation for upcoming 6.30.0 release. These are all documentation and CI changes with the exception of #1247 which is a bugfix but is zero risk as all it does is explicitly check objects are None before calling their member functions.

• Fixed error accessing sys.stdout/sys.stderr when those are None #1247
• Copy payloadpage.page from IPython #1317
• Remove downstream_check #1318
• Remove link to numfocus for funding. #1320
• Don't rerun test with --lf it hides failures. #1324
• Test more python versions #1358
• Update pre-commit and github actions #1401