Use actions/checkout feature to fetch all commits

Setting the "fetch-depth" to a positive value fetches that many
commits back (and the default value is 1), but setting it to 0
fetches all commits, as in a (deep) normal fetch.

.github/workflows/pythonpackage.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
       with:
-        fetch-depth: 1000
+        fetch-depth: 0
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4
       with: