Auto merge of #19205 - asajeffrey:test-perf-add-error-message, r=edunham

Add 'Error loading page' case for validating correctness of test-perf data

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Add case for `Error loading page` title to test-perf runner.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because this is test infrastructure

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etc/ci/performance/runner.py

@@ -127,7 +127,7 @@ def parse_log(log, testcase, url):
     def valid_timing(timing, url=None):
         if (timing is None or
                 testcase is None or
-                timing.get('title') == 'Error response' or
+                timing.get('title') == 'Error loading page' or
                 timing.get('testcase') != url):
             return False
         else: