ci: run setup-python before actions-operator to fix tox install

Github's rollout of 24.04 for ubuntu-latest has now reached
python-libjuju, so `pip install tox` no longer works -- 24.04 prevents
installing packages using pip. This causes an error with in 'Setup
operator environment' using charmed-kubernetes/actions-operator@main.
The fix is to run our 'Setup Python' step using actions/setup-python
before actions-operator instead of after.

Since this takes care of installing tox, we can remove pip install tox
for the jobs using these steps.

Also bump setup-python to v5 for integration-quarantine, matching the
recent PR bumping the version for other jobs.

.github/workflows/test.yaml

@@ -79,6 +79,10 @@ jobs:
     steps:
       - name: Check out code
         uses: actions/checkout@v4
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python }}
       - name: Setup operator environment
         uses: charmed-kubernetes/actions-operator@main
         with:
@@ -112,12 +116,6 @@ jobs:
       #     # set model defaults
       #     juju model-defaults apt-http-proxy=$PROXY apt-https-proxy=$PROXY  juju-http-proxy=$PROXY juju-https-proxy=$PROXY  snap-http-proxy=$PROXY snap-https-proxy=$PROXY
       #     juju model-defaults
-      - name: Setup Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: ${{ matrix.python }}
-      - name: Install dependencies
-        run: pip install tox
       - name: Run integration
         # Force one single concurrent test
         run: tox -e integration
@@ -134,16 +132,14 @@ jobs:
     steps:
       - name: Check out code
         uses: actions/checkout@v3
+      - name: Setup Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python }}
       - name: Setup operator environment
         uses: charmed-kubernetes/actions-operator@main
         with:
           provider: lxd
           juju-channel: 3.4/stable
-      - name: Setup Python
-        uses: actions/setup-python@v4
-        with:
-          python-version: ${{ matrix.python }}
-      - name: Install dependencies
-        run: pip install tox
       - name: Run integration
         run: tox -e integration-quarantine

tox.ini

@@ -1,6 +1,7 @@
 # Tox (http://tox.testrun.org/) is a tool for running tests
 # in multiple virtualenvs. This configuration file will run the
 # test suite on all supported python versions. To use it, "pip install tox"
+# (pre ubuntu 24.04 -- otherwise consider using pipx or apt instead of pip)
 # and then run "tox" from this directory.
 
 [tox]