fix(vim): use vimscript comment syntax for blockinfile markers in vimrc

roles/configuration/tasks/extras.yml

@@ -9,7 +9,7 @@
       set smartindent
       set mouse=a
     insertafter: EOF
-    marker: "# {mark} CUSTOM VIM CONFIG"
+    marker: "\" {mark} CUSTOM VIM CONFIG"
   failed_when: false
 
 # Tuned for VM workloads: low swappiness, aggressive writeback, large page-cluster