Rust: add to `labeler.yml

Author: Paolo Tranquilli

Diff for: .github/labeler.yml

@@ -30,6 +30,10 @@ Ruby:
   - ruby/**/*
   - change-notes/**/*ruby*
 
+Rust:
+  - rust/**/*
+  - change-notes/**/*rust*
+
 Swift:
   - swift/**/*
   - change-notes/**/*swift*