Update book_stable.yml

Author: jorgensd

.github/workflows/book_stable.yml

@@ -16,7 +16,7 @@ env:
 jobs:
   build-book:
     runs-on: ubuntu-latest
-    container: ghcr.io/fenics/dolfinx/lab:v0.8.0
+    container: ghcr.io/fenics/dolfinx/lab:stable
 
     env:
       PYVISTA_TRAME_SERVER_PROXY_PREFIX: "/proxy/"