flaky project manager test

[johrstrom]

This test keeps failing in our CI. Not 100% of the time, but enough to be annoying. Seems there's some race condition that's flaky. This ticket is to correct this test case so that it always passes.

Image]: /home/runner/work/ondemand/ondemand/apps/dashboard/tmp/screenshots/failures_test_submitting_launchers_from_a_template_project_works.png
E

Error:
ProjectManagerTest#test_submitting_launchers_from_a_template_project_works:
Errno::ENOTEMPTY: Directory not empty @ dir_s_rmdir - /tmp/d20230327-5863-1nrrld
    test/system/project_manager_test.rb:925:in `block in <class:ProjectManagerTest>'

rails test test/system/project_manager_test.rb:924