* lisp/msb.el: Use lexical-binding

Remove redundant `:group` args.
(msb--add-to-menu): Strength-reduce `eval` to `symbol-value` and use `push`.
(msb--create-sort-item): Strength-reduce `eval` to `symbol-value`.
(msb-menu-bar-update-buffers): Replace `(lambda...) with a proper closure.
3 jobs for master in 10 minutes and 40 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Fast
passed #16441
test-fast-inotify

00:06:44

 
  Normal
passed #16442
test-lisp-inotify

00:03:55

passed #16443
test-lisp-net-inotify

00:03:29