0.12.6 release candidate

All packages were built and uploaded automatically as a part of this run. Compared to 0.12.5, the only target not present is macos-carbon as there's no way to get it working with recent macOS / XCode versions available in CI -- on the other hand, quite a few targets have been added 🎉

Considering they were built in a clean environment (as opposed to the maintainer’s machine, which was done in previous releases), checksums/signature will not be provided for this release.

Builds for centos8-ppc64 and stretch-armel failed due to timeout errors twice (see earlier run), will probably be moved to self-hosted runner for the final release.