ci: create a new test-on-pr CI workflow without Codecov, headless testing, and build installation

[bobleesj]

Addresses scikit-package/scikit-package-system#4

For level-4 in skpkg, I think it's much simpler to create a new workflow file... the existing test-on-pr is a bit complicated logic dealing with headless testing, install build packages, codecov, etc.

I am also thinking that some users may just want to copy this simple test-on-pr and implement it on their own packages too.

[bobleesj]

@sbillinge this is ready for review. I will first test this once merged to main. Then I will ask for another PR from main to v0 once tested.

[sbillinge]

Just a quick question. To avoid copy-pasted code (which we know we don't like) should we think for a second whether it is better to do this by having each block of code in only one place in this repo and then just calling things when they are wanted. i.e., we have this file and and another one with just the non codecov, non headless

[bobleesj]

should we think for a second whether it is better to do this by having each block of code in only one place in this repo

Indeed, this might be possible. Like currently we do use snippets in our docs where it contain reusable blocks of instructions like scikit-package installation steps which occur thoruhgout Level3-5.

I created an issue here: #144