docs: fix param name in gtk_source_search_settings_set_search_text()
docs: fix param name in gtk_source_search_settings_set_search_text()

https://bugzilla.gnome.org/show_bug.cgi?id=785536

GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview