Use pre-commit directly in the formatting tox job

Will prevent change in one of the script to affect the other one

Author: Pierre-Sassoulas

tox.ini

@@ -36,11 +36,11 @@ commands =
 [testenv:formatting]
 basepython = python3
 deps =
-    black==20.8b1
-    isort==5.5.2
+    pre-commit
+    sphinx
+    pytest
 commands =
-    black --diff --check . --exclude="tests/functional/|tests/input|tests/extensions/data|tests/regrtest_data/|tests/data/|venv|astroid|.tox"
-    isort . --check-only
+    pre-commit run --all-files
 changedir = {toxinidir}
 
 [testenv:mypy]