Use python -m instead pip directly.

It's recommend to use this way. With tox is not really necessary to do
it but it can be good to use it. See this article[1], For example python -m pip executes pip using the Python interpreter you specified as python.

[1] https://snarky.ca/why-you-should-use-python-m-pip/

Change-Id: Ie4be214cce624bc73b8d6661ed459becb418ffa0

tox.ini

@@ -118,7 +118,7 @@ allowlist_externals =
     bash
 commands_pre =
     ansible-galaxy collection install ansible.posix containers.podman
-    pip install -q bindep fixtures
+    python -m pip install -q bindep fixtures
     bindep test
 commands =
     pytest --color=no \