ci: add whitespace check

[Alizter]

This adds a whitespace check to the CI that fails if there is trailing white space or a file does not end with a newline.

[jdchristensen]

I thought it was pretty funny that in an earlier version, whitespace.yml didn't end in a newline... 😄

[Alizter]

@jdchristensen OK sorry for the noise. I think I'm done with this sprint. The first commit adds the CI checks. The second fixes the end newlines and the third fixes the trailing white spaces. Just to be sure I will push each commit separately again.

[Alizter]

Here is the first commit, it should fail the check as there are trailing whitespaces in the library. And it does.

[Alizter]

Here is the second commit, it should fail because only the trailing white spaces have been fixed but there are still problems with the end newlines.

[Alizter]

Here is the third commit. The end newlines have now been fixed and all the checks pass.

[Alizter]

Once we merge this, I'll prepare a PR that ignores these commits from git blame so that there aren't spurious blames everywhere and our history is clean. I can't do that now as the hash might change.

[Alizter]

Oh and I forgot to drop the commit removing the whitespace, here is that done now.

[jdchristensen]

@Alizter, thanks for figuring out how to do this. Is it easy to do something like git diff --check master...HEAD to do the check on the entire diff? (Maybe master...HEAD would need to be replaced with foo HEAD, where foo is the starting commit of the PR? Not sure the context this is run in.)

[Alizter]

@jdchristensen We have a shallow clone of the commits in the PR when doing the whitespace checks. I'll see if I can make it a single check rather than iterating over each commit.

Hmm actually this depends on whatever git log outputs rather than going over each commit. Let me ponder on it some more.

[Alizter]

I got something sort-of working, but I can't get github actions to print the commit, file and location of the whitespace. I am out of energy for today, so I will take another look later.