[llvm] [Release] Add keith to valid archive uploaders (PR #106018)

[Tom Stellard via llvm-commits]

tstellar wrote:

If @tru agrees then I don't have an object to uploading a 18.1.8 binary, since the policy was meant for LLVM 19+.  However, @keith I would prefer if the script was modified so that it  matched both your username and the binary name when checking for a valid uploader.  You don't need to make the change for all users, just for you and this upload. 

https://github.com/llvm/llvm-project/pull/106018