CI: fix artifact name for Cygwin

[oech3]

tag/latest-commit 's artifacts are no longer updatesince the tag is Immutable.
Let rename it to main.

Closes #12520

https://github.com/uutils/coreutils/releases/tag/latest-commit should be manually removed by maintainer for #13839 after this was merged.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[xtqqczze]

Sorry, having both a tag and a branch named main is unnecessarily confusing.

[oech3]

Why? If artifacts are exactly coming from main, it is the best name.

[oech3]

I reverted tag. Previous artifacts should be manually removed (it is impossilbe to do via PR).