Alter CODEOWNERS file to switch required PR review team

The intention being that we can choose to expand our pool of senior reviewers beyond just the current maintainers.

I hope expanding this pool might help tackle the PR review mountain somewhat over time.

Author: MyreMylar

.github/CODEOWNERS

@@ -6,4 +6,4 @@
 # example. The documentation can be seen here:
 # https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
 
-* @pygame-community/pygame-contributing-admins
+* @pygame-community/pygame-senior-reviewers