Update pipeline CEL expression

so that it can be copied verbatim to release branches. I.e. there
will be no diff in CEL expressions between `master` and `release-*`
branches with such a CEL expression.

Less diff -> simpler life when setting up release.

.tekton/collector-build.yaml

@@ -10,10 +10,7 @@ metadata:
     pipelinesascode.tekton.dev/max-keep-runs: "500"
     pipelinesascode.tekton.dev/on-cel-expression: |
       event == "pull_request" || (
-        event == "push" && (
-          source_branch == "master" ||
-          target_branch.startsWith("refs/tags/")
-        )
+        event == "push" && target_branch.matches("^(master|release-.*|refs/tags/.*)$")
       )
   labels:
     appstudio.openshift.io/application: acs