Add a work-flow to run nightly tests of dpctl

[oleksandr-pavlyk]

This workflow runs nightly, install dpctl from
dppy/label/dev, and runs tests

This ensures tests are run even if no development happens. The intent is it might catch issues due to external dependency updates, and such.

The work-flow can also be triggered manually.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[coveralls]

coverage: 87.725%. remained the same
when pulling 94c6061 on add-cron-job-to-run-tests
into 9b3341a on master.

[github-actions]

Array API standard conformance tests for dpctl=0.19.0dev0=py310hdf72452_250 ran successfully.
Passed: 894
Failed: 1
Skipped: 119