test: Disable unwanted tracebacks on pytest xfails

pytest-dev/pytest#11233 overloaded pytest's summary parameter to make it
also add tracebacks for xfailed tests. This makes finding the real
failures amongst the new xfail error messages painful. Disable this
which unfortunately means that we also loose the xfails and xpasses from
the short test summary.

setup.cfg

@@ -167,7 +167,7 @@ filterwarnings =
 #
 #   pytest -k test_name
 #
-addopts = "-v" "-rsxXfE" "--doctest-glob="
+addopts = "-v" "-rsfE" "--doctest-glob="
 
 markers =
     darwin: only run on macOS