Set up venv for build action

.forgejo/workflows/build.yaml

@@ -42,6 +42,8 @@ jobs:
           cache: pip
       - name: Set up Python environment
         run: |
+          python3 -m venv venv
+          source venv/bin/activate
           curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
           python3 get-pip.py
           python3 -m pip install -r requirements.txt