qa: fix error reporting string in assert_cluster_log

Fixes: https://tracker.ceph.com/issues/63217
Signed-off-by: Dhairya Parmar <dparmar@redhat.com>

Author: dparmar18

qa/tasks/ceph_test_case.py

@@ -255,7 +255,7 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 
                 if present and not self.match():
                     log.error(f"Log output: \n{self.watcher_process.stdout.getvalue()}\n")
-                    raise AssertionError(f"Expected log message found: '{expected_pattern}'")
+                    raise AssertionError(f"Expected log message not found: '{expected_pattern}'")
                 elif fail or (not present and self.match()):
                     log.error(f"Log output: \n{self.watcher_process.stdout.getvalue()}\n")
                     raise AssertionError(f"Unexpected log message found: '{expected_pattern}'")