Install `dpctl` package from dedicated channel in coverage GitHub action

[antonwolfy]

This PR is a temporary workaround to unblock Coverage action until dpnp is updated to support the latest dpctl where asynchronous execution is implemented.

• [x] Have you provided a meaningful PR description?
• [ ] Have you added a test, reproducer or referred to 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?
• [ ] If this PR is a work in progress, are you filing the PR as a draft?

[github-actions[bot]]

View rendered docs @ https://intelpython.github.io/dpnp/index.html