Fix test issue caused by previously cloned fre-workflows

[ceblanton]

Describe the bug
In a previous failed test run, test_configure_script (which temporarily overrides HOME) crashed before restoring HOME. This caused the subsequent test_cli_fre_pp_checkout_case to run fre pp checkout with HOME pointing at fre/pp/tests/configure_yaml_out/, cloning the entire fre-workflows repo (including its own lib/python/tests/) into configure_yaml_out/cylc-src/FOO__BAR__BAZ/. On the next test run, pytest collected those tests — which then failed because they expect to run from inside the checkout directory.

To Reproduce
Pretend to be a test_cli_fre_pp_checkout_case test that fails, by manually cloning fre-workflows to re/pp/tests/configure_yaml_out/cylc-src/FOO__BAR__BAZ.

mkdir -p fre/pp/tests/configure_yaml_out/cylc-src/FOO__BAR__BAZ
git clone https://github.com/NOAA-GFDL/fre-workflows.git fre/pp/tests/configure_yaml_out/cylc-src/FOO__BAR__BAZ

Then run pytest

Expected behavior

Additional context
Add any other context about the problem here.