[Emacs] Faster mu4e update if no need to invoke mbsync

org/config/emacs.org

@@ -1718,6 +1718,11 @@ configuration for the ~mu4e~ package itself.
   (defmacro mu4e-view-mode--prepare ()
     `(lambda () (visual-line-mode 1)))
   :gfhook ('mu4e-view-mode-hook (mu4e-view-mode--prepare))
+  :general
+  (phundrak/evil
+    :keymaps 'mu4e-main-mode-map
+    :packages 'mu4e
+    "U" #'mu4e-update-index)
   :config
   (require 'mu4e-view)
   (with-eval-after-load 'mm-decode