test: remove unnecessary image prefetch for chainsaw tests

Only prefetch images actually used by the test: pgbackrest and postgres.
Removes ~500MB of unused images (pgbouncer, pgadmin, exporter, upgrade).

Author: sfc-gh-jmckulka

.github/workflows/test.yaml

@@ -99,13 +99,8 @@ jobs:
           k3s-channel: "${{ matrix.kubernetes }}"
           prefetch-images: |
             registry.developers.crunchydata.com/crunchydata/crunchy-pgbackrest:ubi9-2.56.0-2542
-            registry.developers.crunchydata.com/crunchydata/crunchy-pgbouncer:ubi9-1.24-2542
-            registry.developers.crunchydata.com/crunchydata/crunchy-postgres-exporter:ubi9-0.17.1-2542
             registry.developers.crunchydata.com/crunchydata/crunchy-postgres:ubi9-17.6-2542
             registry.developers.crunchydata.com/crunchydata/crunchy-postgres:ubi9-16.10-2542
-            registry.developers.crunchydata.com/crunchydata/crunchy-upgrade:ubi9-18.0-2542
-            registry.developers.crunchydata.com/crunchydata/crunchy-pgadmin4:ubi9-9.8-2542
-            registry.developers.crunchydata.com/crunchydata/postgres-operator:ubi9-5.8.4-0
 
       - name: Get pgMonitor files.
         run: make get-pgmonitor