Improve tests for gio file notifications

Improve tests for gio file notifications

* .gitlab-ci.yml (test-filenotify-gio): Call "make -k".

* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-file-notify-add-watch):
Set connection property "gio-file-monitor".

* lisp/net/tramp-sh.el (tramp-get-remote-gio-file-monitor): New defun.
(tramp-sh-handle-file-notify-add-watch): Use it.

* test/lisp/filenotify-tests.el (file-notify--test-read-event): Simplify.
(file-notify--test-monitor): Handle also remote "gio monitor".
(file-notify-test03-events, file-notify-test04-autorevert)
(file-notify-test05-file-validity, file-notify-test08-backup)
(file-notify-test09-watched-file-in-watched-dir):
Handle GKqueueFileMonitor.