Make tests run in parallel on GitHub actions

tests/requirements.txt

@@ -5,3 +5,4 @@ camoufox
 werkzeug<3.0.0
 pytest-httpbin==2.1.0
 httpbin~=0.10.0
+pytest-xdist

tox.ini

@@ -14,7 +14,7 @@ deps =
 commands =
     playwright install-deps chromium firefox
     camoufox fetch --browserforge
-    pytest --cov=scrapling --cov-report=xml
+    pytest --cov=scrapling --cov-report=xml -n auto
 
 [testenv:pre-commit]
 basepython = python3