[llvm] [Github] Add build Flang docs in CI if autogenerated files change (PR #72721)

[Kiran Chandramohan via llvm-commits]

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

Thanks. We probably have to add the HLFIR dialect ops as well. But that can come in a separate patch since it is not yet added to the documentation.

https://github.com/llvm/llvm-project/pull/72721