Try installing pip for action

.forgejo/workflows/build.yaml

@@ -40,6 +40,8 @@ jobs:
         uses: actions/setup-python@v5
         with:
           cache: pip
+      - name: Install pip
+        run: python3 -m ensurepip
       - name: Set up Python environment
         run: python3 -m pip install -r requirements.txt
       - name: Set up Rust