minor api issues

["Matthias Clasen" <matthiasc poet de>]

While looking through the glib SGML documentation,
I found a couple of minor API issues:

1) the third parameter to GScannerMsgFunc is declared as gint, but should
   clearly be a gboolean (#61468).

2) g_scanner_add/remove/foreach_symbol are documented as deprecated,
    but not guarded by G_DISABLE_DEPRECATED (#61469).

3) The documentation for G_CONST_RETURN says that it should not be
    used for function arguments, but g_get_charset nevertheless does so.
    gtk-doc follows the documentation and chokes on the g_get_charset
prototype
    (reported as a gtk-doc bug, #61341, but maybe it is really a glib API
bug).

Matthias