Bug 1758204: mozunit should use --tb=short with pytest r=ahal

This will decrease test output clutter while making it easier to
identify and diagnose test failures.

Differential Revision: https://phabricator.services.mozilla.com/D140421

config/mozunit/mozunit/mozunit.py

@@ -317,6 +317,7 @@ def main(*args, **kwargs):
                 "-c",
                 os.path.join(here, "pytest.ini"),
                 "-vv",
+                "--tb=short",
                 "-p",
                 "mozlog.pytest_mozlog.plugin",
                 "-p",