Terminate isearch when point has moved to another buffer

* lisp/isearch.el (isearch-post-command-hook): Terminate isearch
when the command just executed has moved point to another buffer.
https://lists.gnu.org/archive/html/emacs-devel/2021-04/msg00309.html
3 jobs for master in 9 minutes and 25 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Fast
passed #16584
test-fast-inotify

00:06:33

 
  Normal
passed #16585
test-lisp-inotify

00:02:52

passed #16586
test-lisp-net-inotify

00:02:20