ci: use container-rpmbuilder image (#3)

CI images move off the packer-images monorepo to semver-released container-* repos.

- run RPM build steps on docker-internal/rpmbuilder:0.1.0-alma9

Reviewed-on: #3
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

.woodpecker/release.yml

@@ -18,7 +18,7 @@ steps:
             cpu: 2
 
   - name: package
-    image: git.unkin.net/unkin/almalinux9-rpmbuilder:latest
+    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/rpmbuilder:0.1.0-alma9
     commands:
       # build-rpm.sh prints "PLUGIN_SHA256 <binary> <version> <sha>" for the
       # Puppet plugin registration pin.