Fixes preflight-checks.py

[ellensp]

Description

After #21361 preflight-checks.py no longer advises of what env's to use.

Function get_envs_for_boardents() in preflight-checks.py returns a list of environment names but without the needed prefix, this resulted in preflight-checks.py not listed available environments to use.
Function check_envs() updated to use osregex.

Benefits

Works as was intended.

Related Issues

issue #21363

[ellensp]

well that didn't work... marking draft till I work out what went wrong.

[ellensp]

@thinkyhead hopefully this fix doesn't break what you where trying to do with osregex... please check.

[thisiskeithb]

This still fails on one of the beta boards/environments I'm testing (so I can't post details), but works for others.

It'd be better to revert #21361

Edit: @rhapsodyv has some ideas that'll remove the need for this board’s custom variant, so it might be a moot point.

[kad]

It'd be better to revert #21361

I'd really suggest to revert.
Once you will be able to publish example lines of those undisclosed build targets, I volunteer to update script to handle those.
Or just open issue with proposed example of how line would look line with same faked values and assign to me, I'll do script update for those..

[ellensp]

going with revert.

[thinkyhead]

ended up going with fix. #21372