pool: Add a unit test for the old pool API

[epmikida]

This API is still used by some users according to issue so we want to make sure it is still tested. See #355.

[epmikida]

The added test passes, however there are some warnings cause I am currently using the new API for creating the pool def struct. I'm not sure how to create the pool def struct using the old API.

[shintaro-iwasaki]

@epmikida Thank you for your contribution! Please use the old API to check the old pool behavior. The following is an example (note: the latest example uses the new API): https://github.com/pmodels/argobots/blob/v1.1/examples/scheduling/sched_and_pool_user.c

Please feel free to ask me any questions.

[shintaro-iwasaki]

Note: I relaxed the GitHub Action restriction, so the basic CI checks should run automatically when you push/rebase commits to your local branch registered to this PR.