Fix the automated Dromaeo test runner. Without this change, it sits spinning at 100% CPU usage after completing all the tests.
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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 fix#11843 (github issue number if applicable).
- [X] These changes do not require tests because we don't run the Dromaeo tests in automation.
Source-Repo: https://github.com/servo/servo
Source-Revision: 851194b0033cb1daa15d99adbb0191b25b637fa8
This reverts commit c315404db80c92a695531b0aa4bcf61c125a3bff, reversing
changes made to b00583bd4e7169a6b952633df718268904f2bd0c.
Source-Repo: https://github.com/servo/servo
Source-Revision: 47d6d958f58f5011742a18abcdd5a76bf4390966