Add missing makedepends glib2-devel

Configuring config.h using configuration
Build-time dependency glib-2.0 found: YES 2.82.2
Program /usr/bin/glib-genmarshal found: NO

seahorse-nautilus/tool/meson.build:1:19: ERROR: Dependency 'glib-2.0' tool variable 'glib_genmarshal' contains erroneous value: '/usr/bin/glib-genmarshal'

This is a distributor issue -- please report it to your glib-2.0 provider.

A full log can be found at /build/seahorse-nautilus/src/build/meson-logs/meson-log.txt

glib_genmarshal has been moved to glib2-devel, so include that.