llvmlite 0.42.0 Checklist

llvmlite 0.42.0

[x] ~Cherry-pick items from the 0.42.0 milestone into a PR targeting the release branch.~ N/A, no changes required.
[x] Update CHANGE_LOG on cherry-pick-PR (#1029).
[x] ~Have cherry-pick-PR reviewed and merged.~ none
[x] Test HEAD of release branch on buildfarm (pre-tag testing):
- [x] conda package build and test.
- [x] wheel build.
[x] Annotated tag v0.42.0 on release branch (llvmlite tags DO have a v prefix).
[x] Build and upload conda packages on buildfarm (check "upload"). llvmlite_272
[x] Build wheels and sdist on the buildfarm (check "upload"). llvmlite_wheel_60
[x] Verify packages uploaded to Anaconda Cloud and copy to numba/label/main.
[x] Upload wheels and sdist to PyPI. (upload from ci_artifacts).
[x] Verify wheels for all platforms arrived on PyPi.
[x] Verify ReadTheDocs build.
[x] Send RC/FINAL announcement email / post announcement to discourse group.
[x] Post link to Twitter and Mastodon and anywhere else that is appropriate.

[x] Cherry-pick changes to the CHANGE_LOG to main. (FINAL ONLY) https://github.com/numba/llvmlite/pull/1032
[x] Clean up ci_artifacts by moving files to subdirectories
[x] Update release checklist template with any additional bullet points that may have arisen during the release.
[x] Ping Anaconda Distro team to trigger a build for defaults (FINAL ONLY).
[x] Close milestone (and then close this release issue).