Update build_docs.yml

fix permission denied

Author: C-Achard

.github/workflows/build_docs.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - run: apt-get update && apt-get install libgl1
+    - run: sudo apt-get update && sudo apt-get install libgl1
     - uses: actions/checkout@v1
     # Standard drop-in approach that should work for most people.
     - uses: ammaraskar/sphinx-action@master