CI: Backport the CI to the 11.8.x branch

[leofang]

• Strip the steps building cuda.core; let's build cuda.bindings only
• By the time the test CI is ready, we test cuda.bindings (11.8.x) built in this branch + cuda.core built in the main branch (since we do not need to back port cuda.core changes)

[leofang]

I think perhaps back porting is overkill. Looking at the current CI trigger conditions:

cuda-python/.github/workflows/ci-gh.yml

Lines 7 to 11 in 0ca509e

	on:
	push:
	branches:
	- "pull-request/[0-9]+"
	- "main"

• For PR: any changes in a PR targeting the 11.8.x branch should also trigger the pipeline
• After PR merge: We probably can just add the 11.8.x branch there, so that the post merge artifacts can be produced.

Another thing is we'll need to use a different CTK version based on the target branch. GHA should have a way for us to detect it inside the workflow or action.