Inspect PR changes to determine if subproject builds are needed.

[alliepiper]

Subprojects: libcudacxx cub thrust

Dependencies:
  - libcudacxx -> cccl
  - cub -> cccl libcudacxx thrust
  - thrust -> cccl libcudacxx cub

Base SHA: e3758cfa45ebde29893a149933efbb7071fac56
HEAD SHA: a7f6ff444ab9fb38000d11ba3a3fef4f292b3df5

Dirty files:
  - .github/actions/compute-matrix/compute-matrix.sh
  - .github/workflows/pr.yml
  - ci/inspect_changes.sh

Modifications in project?
X - non-project files
  - libcudacxx
  - cub
  - thrust

Modifications in project or dependencies?
X - libcudacxx
X - cub
X - thrust

LIBCUDACXX_DIRTY=true
CUB_DIRTY=true
THRUST_DIRTY=true

[alliepiper]

The copy-pr-bot doesn't expose base SHA information. I've filled an issue with them to see if they can somehow expose that info to us.

[miscco]

I dont know who, but I guess there is a way to transform this into a

Suggested change

	if dirty_files | grep -v -E "${subprojs_grep_expr}" | grep -q "."; then
	return 1
	else
	return 0
	fi
	return dirty_files | grep -v -E "${subprojs_grep_expr}" | grep -q "."; | SOMETHING

[jrhemstad]

Approving since none of my comments were blocking.