[llvm] github: Add tablegen directories to PR autolabeler (PR #109129)

[Anton Korobeynikov via llvm-commits]

asl wrote:

> Maybe eventually if Github lets you do label-based subscriptions for PRs, but I believe they only support that for issues currently. That's still how notifications are done currently as far as I can tell.

Yeah. Sadly, PRs are for some reason unknown to me are excluded from label-based subscriptions and notifications.

https://github.com/llvm/llvm-project/pull/109129