ci: add condition for CI to run on PRs or main

Author: Meow404

.cirrus.yml

@@ -1,5 +1,6 @@
 registry_config: ENCRYPTED[!88cf0d757d2f8b93dca9e57dc166b65ddedef6378e7ac12a91a022ab3fb28dd47b10d452dc5c53a68e144e6bdbae999b!]
 jammy_task:
+  only_if: "$CIRRUS_PR != ''  || $CIRRUS_BRANCH == 'main'" # This condition ensures the task runs only for PRs or on the main branch.
   timeout_in: 120m
   container:
     image: ghcr.io/dairlab/docker-dair/jammy-dair-base:v1.42
@@ -29,6 +30,7 @@ jammy_task:
     format: junit
 
 noble_task:
+  only_if: "$CIRRUS_PR != ''  || $CIRRUS_BRANCH == 'main'" # This condition ensures the task runs only for PRs or on the main branch.
   timeout_in: 120m
   container:
     image: ghcr.io/dairlab/docker-dair/noble-dair-base:v1.42