gh-101758: Add a Test For Single-Phase Init Module Variants by ericsnowcurrently · Pull Request #101891 · python/cpython

…h-101969)

gh-101891 is causing failures under `$> ./python -m test test_imp -R 3:3`.  Furthermore, with that fixed, "test_singlephase_variants" is leaking references.  This change addresses the first part, but skips the leaking tests until we can follow up with a fix.

#101758