test: skip a test on pypy
test: skip a test on pypy

I thought I knew when this passed and when it failed. Now that our tests
are not TestCase's, pytest is enforcing the xfails.  This passes locally
on Mac, but fails in CI on Mac.  So skip it.

nedbat/coveragepy,nedbat/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,hugovk/coveragepy,nedbat/coveragepy