Modify build matrix for community nightlies

Updated the build matrix to include new platforms and remove deprecated ones.

Author: ihalatci

.github/workflows/build-citus-community-nightlies.yml

@@ -23,13 +23,11 @@ jobs:
       fail-fast: false
       matrix:
         platform:
-          - el/7
           - el/8
-          - ol/7
-          - debian/bullseye
+          - el/9
+          - ol/9
           - debian/bookworm
           - debian/trixie
-          - ubuntu/bionic
           - ubuntu/noble
           - ubuntu/jammy