Upgrade PDM I guess?

Author: Tinche

.github/workflows/main.yml

@@ -27,7 +27,7 @@ jobs:
           python-version: "${{ matrix.python-version }}"
           allow-python-prereleases: true
           cache: true
-          version: "2.19.2"
+          version: "2.21.0"
 
       - name: "Run Tox"
         run: |
@@ -113,7 +113,7 @@ jobs:
       - uses: "pdm-project/setup-pdm@v4"
         with:
           python-version: "3.12"
-          version: "2.19.2"
+          version: "2.21.0"
 
       - name: "Install check-wheel-content and twine"
         run: "python -m pip install twine check-wheel-contents"