Fix jalview.gui.QuitHandlerTest.testSavedProjectChanges and testSavedAlignmentChanges test failing on build server

These two tests are failing on the build server:
https://builds.jalview.org/browse/JB-GDB-JOB1-458/test

They are similar tests that attempt to:
1) set the saved state of an alignment to false.
2) run a save (without any delay) (in same thread).
3) perform a quit with the default mock response set to "Cancel".
4) check the quit result.

Because the save in step 2 should complete before the quit is performed, the saved state should become true, and the quit should NOT produce any interactive popups, meaning that the end result should be QUIT. If a popup is produced, then the mock response would be Cancel, and so the end result would be CANCEL_QUIT.

The failing tests are showing the result is CANCEL_QUIT, so my guess is that the file is not completing its save, but the thread is continuing anyway.
A simple Thread.sleep(1000) after the save didn't fix it, so trying something more substantial than that.
Unfortunately the error is only being observed on the build server so it's difficult to diagnose.