Use firedrake vanilla docker images, which now runs under the root user

Author: francesco-ballarin

.github/workflows/website.yml

@@ -34,18 +34,16 @@ jobs:
             notebook_pattern: |
               "**/tutorial_*_dolfinx.ipynb"
           - backend: firedrake
-            container: firedrakeproject/firedrake
+            container: firedrakeproject/firedrake-vanilla-default
             setup_container: |
               export DEBIAN_FRONTEND="noninteractive"
               apt update -y -q
               apt install -y -qq xvfb
-              echo "/home/firedrake/firedrake/bin" >> $GITHUB_PATH
+              rm /usr/lib/python3.*/EXTERNALLY-MANAGED
             notebook_pattern: |
               "**/tutorial_*_firedrake*.ipynb"
       fail-fast: false
-    container:
-      image: ${{ matrix.container }}
-      options: --user root
+    container: ${{ matrix.container }}
     steps:
       - name: Determine which branch to checkout when cloning source repository
         id: source_branch