Adding Rocky/RHEL 9 to Linux CI tests

[simtheverse]

Since RHEL/Rocky9 are supported OSs, I wanted to encourage adding them to the matrix for linux CI testing: https://github.com/nasa/trick/blob/master/.github/workflows/test_linux.yml

[brendan-nasa]

it's not a top priority for us at the moment, but if you'd like to put together a pr for this, it would be a great thing to have before the end of year!

[simtheverse]

Sounds good, tried my hand at it in #2007.