chore: replace old ruby teams with cloud-sdk-ruby-team (googleapis#389)

b/479546763

Author: suztomo

.github/CODEOWNERS

@@ -4,4 +4,4 @@
 # For syntax help see:
 # https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners#codeowners-syntax
 
-*     @googleapis/ruby-team @olavloite @rahul2393 @ansh0l
+*     @googleapis/cloud-sdk-ruby-team @olavloite @rahul2393 @ansh0l