ci: Use composite actions for tutorials

Author: JDBetteridge

.github/actions/docker-build/action.yaml

@@ -14,7 +14,6 @@ inputs:
   base:
     description: "Base docker image to build on top of"
     required: true
-    # Update default if docker/Dockerfile.devito ever changes default
     default: "devitocodes/bases:cpu-gcc"
 
 outputs: