[llvm] workflows: Fix release documentation upload (PR #91093)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM.

I'm thinking at some point we might want to refactor this job slightly so that only the final push is in the upload step and let it run on pull requests touching this file, skipping the upload on PR runs?

https://github.com/llvm/llvm-project/pull/91093