add needs (#73)

Author: mscroggs

.github/workflows/docs.yml

@@ -42,6 +42,8 @@ jobs:
   deploy-docs:
     name: Deploy docs to GitHub pages
     runs-on: ubuntu-latest
+    needs:
+      - build-docs
     if: github.ref == 'refs/heads/main'
     environment:
       name: github-pages