Harden SingleDirectoryComponentTest against unexpected module paths

Tested locally by moving XB into a differently named directory, the test fails before but passes with this change.

Happening again, over at #3507330-6: Change ExperienceBuilderController::getHtmlAndBodyAttributes to ::buildHtml → . As predicted, this is gonna slow us down if we don't work around it 😬

And again, at #3507818-13: Tugboat builds failing → . Relieved to see this fixed so quickly!

Automatically closed - issue fixed for 2 weeks with no activity.