Add sponsor button to key repositories

[conejoninja]

Add the sponsor button linking to open collective in the repository.

Needs to be enable ( https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/displaying-a-sponsor-button-in-your-repository )

[leongross]

Interestingly the CI for linux fails, although you did not touch this. I have the same issue in #4517, so dev seems to be broken? Same for nix-test.

[deadprogram]

The fix for nix is in... or at least for the CI. Please rebase against latest dev.

[conejoninja]

done, but now Linux/assert-test-linux fails :/

[leongross]

/usr/bin/ld: ASTContext.cpp:(.text._ZL17DecodeTypeFromStrRPKcRKN5clang10ASTContextERNS3_19GetBuiltinTypeErrorERbb+0x670): undefined reference to `__isoc23_strtoul'

It looks to me as if there is still a version mismatch. The linker is unable to find the symbol __isoc23_strtoul which I think is defined in glibc, so it looks like the glibc version is too old.

[aykevl]

This PR doesn't change any code, so I'd suggest to just ignore the CI errors.
The CI errors are weird though, if they keep happening I think we should do a new llvm-build (by incrementing the cache key) to see whether that helps. It looks like a version mismatch indeed.

[leongross]

I agree @aykevl. Since we had some trouble in the past few days with the CI, I initially thought we should investigate this while we are debugging the CI. But on other PRs like #4517 this could not be observed, so let's get this merged.

[deadprogram]

Thank you @conejoninja now merging.