Fix a bug in the known images test from the locator changes

This was previously looking for namespaces starting with e2e-, my change
flipped it to a contains, which then picked up openshift-e2e-loki, which
does use a external image that we do not want this test failing on.

Restored to a prefix check.

pkg/monitortests/testframework/knownimagechecker/monitortest.go

@@ -136,7 +136,7 @@ func (w *clusterImageValidator) EvaluateTestsFromConstructedIntervals(ctx contex
 			continue
 		}
 		// only look at pull events from an e2e-* namespace
-		if !strings.Contains(event.StructuredLocator.Keys[monitorapi.LocatorNamespaceKey], "e2e-") {
+		if !strings.HasPrefix(event.StructuredLocator.Keys[monitorapi.LocatorNamespaceKey], "e2e-") {
 			continue
 		}