Bring back Windows tests (IAMconsortium#375)

* Bring back Windows tests

* Use windows-latest in GitHub action

* Change back to windows (without '-latest')

* Change venv caching for Windows

.github/workflows/pytest.yml

@@ -15,7 +15,7 @@ jobs:
         shell: bash
     strategy:
       matrix:
-        os: ["macos", "ubuntu"]
+        os: ["macos", "ubuntu", "windows"]
         # keep consistent with py-version badge in README.md and docs/index.rst
         python-version: ["3.10", "3.11", "3.12"]
       fail-fast: false
@@ -44,10 +44,10 @@ jobs:
     #       load cached venv if cache exists
     #----------------------------------------------
     - name: Load cached venv
-      id: cached-poetry-dependencies
+      id: cached-pip-wheels
       uses: actions/cache@v4
       with:
-        path: .venv
+        path: ~/.cache
         key: venv-${{ runner.os }}-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('**/poetry.lock') }}
     #----------------------------------------------
     # install dependencies if cache does not exist