HSEARCH-4920 Don't pre-pull images from elastic docker registry

ci/dependency-update/Jenkinsfile

@@ -63,6 +63,10 @@ def pullContainerImages() {
 		// Cannot use a foreach loop because then Jenkins wants to serialize the iterator,
 		// and obviously the iterator is not serializable.
 		for (int i = 0; i < containerImageRefs.length; i++) {
+			if (containerImageRef.startsWith('docker.elastic.co')) {
+				// an image not from a docker hub, so let's ignore it:
+				continue
+			}
 			containerImageRef = containerImageRefs[i]
 			docker.image(containerImageRef).pull()
 		}