Fix "Update apt cache" handler.

As "update apt cache", it did not match the handler name ("Update apt cache"). The first ansible run failed (https://devops.stackexchange.com/questions/4365/ansible-handler-not-found-on-first-attempt)

roles/containerlab/tasks/main.yml

@@ -4,7 +4,7 @@
     state: present
     filename: netdevops
   notify:
-    - update apt cache
+    - Update apt cache
 
 - name: Install Packages
   ansible.builtin.apt: