Tweak install

Author: martinthomson

.github/workflows/python.yml

@@ -31,7 +31,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install black -r python/requirements.txt
+        pip install black
+        cd python; pip install -r python/requirements.txt
     - name: Reformat
       run: |
         cd python; black --check .