Fix e2e assertion to match new multi-phase error message format

The verifyObservedPhases error message changed from
"resolved content of phase X has changed" to
"resolved content of N phase(s) has changed: phase X (expected...)"
when collecting all mismatches. Update the e2e assertion fragment
to match the new format.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pedjak

test/e2e/features/revision.feature

@@ -572,7 +572,7 @@ Feature: Install ClusterObjectSet
     And ClusterObjectSet "${COS_NAME}" reconciliation is triggered
     Then ClusterObjectSet "${COS_NAME}" reports Progressing as False with Reason Blocked and Message includes:
     """
-      resolved content of phase "resources" has changed
+      resolved content of 1 phase(s) has changed: phase "resources"
     """
     # Restore original content — COS should recover
     When resource "secret/${COS_NAME}-change-secret" is removed