Update to cockpit/pull/21233 testlib

This provides support for shadow DOM test selectors.

Makefile

@@ -33,7 +33,7 @@ COCKPIT_REPO_FILES = \
 	$(NULL)
 
 COCKPIT_REPO_URL = https://github.com/cockpit-project/cockpit.git
-COCKPIT_REPO_COMMIT = c295842a0336c9e967a0c5adc28ddf527876c6c6 # 328
+COCKPIT_REPO_COMMIT = 4fadac0aabdd00e19f4cbf40745091a88a7e58f5 # https://github.com/cockpit-project/cockpit/pull/21233
 
 $(COCKPIT_REPO_FILES): $(COCKPIT_REPO_STAMP)
 COCKPIT_REPO_TREE = '$(strip $(COCKPIT_REPO_COMMIT))^{tree}'