A new pointless fad appeared recently where people just create a fairly
low information tag at the beginning of their github PR titles.
Something like `feat` or other keywords.
This seems to originate from the angular community and to be used for
automation scripts over there. We do not use any of those scripts and if
we did we would be using the github labels, which offer strictly
equivalent functionalities without wasting useful PR title space.
In order for these keywords to fail the validation, I am adding a check
that these directories listed indeed exist in the repository.
Full disclosure: this has been generated by AI. The goal is to have a
quick check that the PR format is correct, before we merge it. This is
to avoid the periodical case when someone forgets to add a milestone or
check the title matches our preferred format.
