[clang] [llvm] [GitHub][CI] Add running of 'dump_ast_matchers.py' to premerge workflow (PR #165472)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

The PR title and description need to be updated. It would be good if the branch gets updated to kick off CI again too.

https://github.com/llvm/llvm-project/pull/165472