We don't need AI/ML features in the tests, so this should reduce CPU
usage by not having the inference process running. Moreover, it prevents
the following lines from being logged in the test output:
```
JavaScript error: resource://gre/actors/MLEngineParent.sys.mjs, line 509: Error: Unable to get the ML engine from Remote Settings.
JavaScript error: resource://gre/actors/MLEngineParent.sys.mjs, line 1279: TypeError: can't access property "postMessage", this[#port] is null
```
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