Update workflow to use Python shell

.github/workflows/update-api-docs.yml

@@ -27,6 +27,7 @@ jobs:
         with:
           image: mathesar/mathesar-dev:latest
           run: ./manage.py spectacular --color --file schema.yml
+          shell: python
 
       - name: Check if schema file has changed
         run: git diff --quiet schema.yml || exit 0