tox: permit positional arguments when running 'unittest'-based unit t…

…ests (#686)

tox.ini

@@ -3,7 +3,7 @@ isolated_build = true
 
 [testenv]
 deps = -r{toxinidir}/requirements-dev.txt
-commands = coverage run -m unittest
+commands = coverage run -m unittest {posargs}
 
 # The system-provided libxml2 on MacOS is typically outdated and this can lead to lxml parsing issues
 # Using PyPi-provided binary wheels instead resolves this