Fix CI bootstrap by switching tests workflow cache to pip

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
-          cache: poetry
+          cache: pip
       - name: Install Poetry
         run: pipx install poetry
       - name: Install dependencies