Add setup-python to "Install tools" Action

We get the following error when we try install pip within CI:

> error: externally-managed-environment
>
> × This environment is externally managed
> ╰─> To install Python packages system-wide, try apt install
>     python3-xyz, where xyz is the package you are trying to
>     install.
>
>     If you wish to install a non-Debian-packaged Python package,
>     create a virtual environment using python3 -m venv path/to/venv.
>     Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
>     sure you have python3-full installed.
>
>     If you wish to install a non-Debian packaged Python application,
>     it may be easiest to use pipx install xyz, which will manage a
>     virtual environment for you. Make sure you have pipx installed.
>
>     See /usr/share/doc/python3.12/README.venv for more information.
>
> note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.

This commit sets up a virtual environment so that pip can install things.

.github/workflows/lint-python.yml

@@ -20,6 +20,11 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v4
 
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.12'
+
     - name: Install tools
       run: pip install pyflakes autopep8 isort pylint