Tests: allow pip 20.1+ build-in-place behavior

Starting with pip 20.1b1+, the *-info subdir appears as a build artifact
under the "local" directory (here, /project). See
- pypa/pip#7555
- pypa/pip#7882
- pypa/pip@ace0c16

tests/helpers/test_common.py

@@ -84,7 +84,6 @@ def test_install_plugin(tmp_path, func):
     assert (targ / "pytest_pdb_break.py").exists()
     targ_egg = next(targ.glob("*-info"))  # dist- (wheel) or egg-
     assert targ_egg.exists()
-    assert next(proj.glob("*-info"), None) is None
 
 
 @pytest.mark.parametrize("wants_symlink", [True, False])