Add 3.20 as a guarded branch

It's an LTS branch, we need it to be guarded.

Author: gsmet

.github/quarkus-github-bot.yml

@@ -38,9 +38,11 @@ triage:
   discussions:
     monitoredCategories: [33575230]
   guardedBranches:
-    - ref: 3.15
+    - ref: '3.20'
       notify: [jmartisk, gsmet, gastaldi, rsvoboda, aloubyansky]
-    - ref: 3.8
+    - ref: '3.15'
+      notify: [jmartisk, gsmet, gastaldi, rsvoboda, aloubyansky]
+    - ref: '3.8'
       notify: [jmartisk, gsmet, gastaldi, rsvoboda, aloubyansky]
   rules:
     - id: amazon-lambda