Post release task for 0.59.1

[sklam]

• cherrypick change-log, remove old towncrier
• cherrypick CI fixes on release branch
• fix towncrier_check.py script

Post-merge:

• update Numba 0.59.1 Checklist #9485

[sklam]

Notes for reviewer:

cherrypick commits from #9480:

• Remove notes from 0.59.0
• Remove release notes for 0.59.1
• Skip test_issue9490_non_det_ssa_problem for PPC
• Reduce thread use to avoid stuck in TBB on machines with high thread …

New commits:

• Get changes for release note and installing.rst from 0.59.1
• Closes #9501. Add link to bug description.
• Update towncrier checker to look into towncrier generated release notes

[esc]

I verified that the cherry-picked 🍒 commits are correct and have the correct diff. I manually inspected the remaining commits to ensure that they are correct. I checked the changes to towncrier_checker.py changes and could confirm, that without these changes, we would end up with a list of false positives on this branch:

 💣 zsh» python maint/towncrier_checker.py --token YYY --beginning 0.59.0dev0 --repo numba/numba
PRs that are missing towncrier notes and not skipped
8990 https://github.com/numba/numba/pull/8990
9048 https://github.com/numba/numba/pull/9048
9058 https://github.com/numba/numba/pull/9058
9089 https://github.com/numba/numba/pull/9089
9123 https://github.com/numba/numba/pull/9123
9126 https://github.com/numba/numba/pull/9126
9140 https://github.com/numba/numba/pull/9140
9141 https://github.com/numba/numba/pull/9141
9144 https://github.com/numba/numba/pull/9144
9154 https://github.com/numba/numba/pull/9154
9169 https://github.com/numba/numba/pull/9169
9189 https://github.com/numba/numba/pull/9189