Flapper test

[andreabergia]

We have a flapper test! In the CI run for my #2186 PR, I have seen the test tests/ecma/Date/15.9.5.8.js ran by MozillaSuiteTest fail: see this run and step.
However, I then submitted an empty commit in my PR, and the test passed.

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Update: there's at least another one from this run: testsrc/tests/ecma/Date/15.9.5.8.js

[rbri]

@andreabergia you can also simply rerun the build from the browser

[andreabergia]

@andreabergia you can also simply rerun the build from the browser

I couldn't find a button. Perhaps only maintainers can?