ci: install requirements.txt into venv before test

.forgejo/workflows/ci.yml

@@ -13,6 +13,9 @@ jobs:
         run: |
           apt-get update -qq
           apt-get install -y -qq python3-venv
-          pip install six pytest
+      - name: prime venv with package + test deps
+        run: |
+          make env
+          env/bin/pip install -r requirements.txt
       - name: test
         run: make test