gi: accept 5 or more the number of signals

It may be increased for later GIO version.

GitHub: #229

Reported by cosmo. Thanks!!!
gi test: fix wrong expected value

https://developer.gnome.org/gio/stable/GApplication.html#GApplication-startup
says the "startup" signal's flags are "Run First".

It requires GObject Introspection 1.40.0 or later because older
GObject Intrpsection has a bug. See also:

  * https://bugzilla.gnome.org/show_bug.cgi?id=709462
  * https://git.gnome.org/browse/gobject-introspection/commit/?id=f6770c808203d4d3eb9a30e5c4bc896f990cae34

GitHub: #229

Reported by cosmo. Thanks!!!