[llvm] [Github] Validate doxygen checksum (PR #202404)

[Jameson Nash via llvm-commits]

vtjnash wrote:

But hold off on merging, since there's some issue with the cmake updates, so will revert (and include this on re-submit) when I can get time to figure out why cmake is confused there https://github.com/llvm/llvm-project/pull/202412

https://github.com/llvm/llvm-project/pull/202404