ci: Install tox using pip instead of apt

[orfeas-k]

Context

Most workflows install tox with thefollowing command https://github.com/canonical/namespace-node-affinity-operator/blob/f8645e2011ca23c7fa32408899e116c27a307f18/.github/workflows/integrate.yaml#L49.
We should instead install using pip since this installs a very old version of tox 3.12.x instead of latest available 4.x.

What needs to get done

Replace
https://github.com/canonical/namespace-node-affinity-operator/blob/f8645e2011ca23c7fa32408899e116c27a307f18/.github/workflows/integrate.yaml#L49
with

          pip install tox

Definition of Done

Tox is installed using pip

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The internal ticket has been created: https://warthogs.atlassian.net/browse/KF-6651.

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[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/KF-6652.

This message was autogenerated