Auto merge of #12484 - aravind-pg:mach, r=ConnorGBrewster

Temporary fix for mach test-{wpt, css} issue with wonky paths

This is just a temporary fix to get `mach test-wpt`, `mach update-manifest` etc. working properly again. A proper fix will likely involve a proper refactoring of the `suite_for_test` function.

<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12481
- [X] These changes have been tested to work locally

r? @ConnorGBrewster cc @jdm

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python/servo/testing_commands.py

@@ -354,7 +354,7 @@ class MachCommands(CommandBase):
             all_handled = True
             for test_path in requested_paths:
                 suite = self.suite_for_path(test_path)
-                if correct_suite != suite:
+                if suite is not None and correct_suite != suite:
                     all_handled = False
                     print("Warning: %s is not a %s test. Delegating to test-%s." % (test_path, correct_suite, suite))
             if all_handled: