Fix the python code style check

For an unknown reason, pip started to install an older version of
prospector which is incompatible with the current pylint. Require the
new prospector version explicitly.

.github/workflows/code_style.yaml

@@ -82,7 +82,12 @@ jobs:
     steps:
       - name: Install prerequisites
         run: |
-          pip install black prospector psutil
+          pip install --upgrade pip
+          # Inexplicably, at some point pip started to insist on installing
+          # prospector==1.7.7, which is incompatible with the new pylint.
+          pip install black prospector==1.8.4 psutil pylint
+          pip list
+          pip list --user
       - name: Checkout source
         uses: actions/checkout@v3
       - name: Run prospector