[ci] Concurrency optimizations

[Grub4K]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

This PR adds a cancel CI running on PRs so that we dont fill up the queue unnecessarily.

It also removes the cancel for master builds, so as to make it queue up neatly one after another. This would result in more frequent builds, and not having to wait for another build to finish for the next push.

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)