Update CODEOWNERS file with specialized team assignment

This updates the CODEOWNERS file to assign the appropriate specialized
maintainer team for pull request reviews, improving the review process
and ensuring domain expertise for code review.

Fixes: flatcar/Flatcar#1791
Team assigned: @flatcar/nebraska-flatcar

Signed-off-by: Jan Bronicki <[email protected]>

Author: John15321

CODEOWNERS

@@ -2,4 +2,4 @@
 # This file defines who is responsible for code review
 # See: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
 
-* @flatcar/flatcar-maintainers
+* @flatcar/nebraska-flatcar