chore: Use clearer error message for match validation atomic errors

[sevenseacat]

Getting an error message like this in a test:

** (Ash.Error.Framework)
     Framework Error

     * Tunez.Music.Album.update must be performed atomically, but it could not be

     Reason: can't atomically match an attribute that is not changing

     See https://hexdocs.pm/ash/update-actions.html#fully-atomic-updates for more on atomics.

Doesn't make it clear what's going on or why. I didn't even realize it was talking about a match validation, not a pattern match!

I think this makes it a little clearer what's going on.

Contributor checklist

• Bug fixes include regression tests
• Chores
• Documentation changes
• Features include unit/acceptance tests
• Refactoring
• Update dependencies

[zachdaniel]

🚀 Thank you for your contribution! 🚀