More const-correctness fixes

This continues one of the const-correctness fixes from the previous
commit (it needed some more transitive fixes), and reverts another of
them, since it was over-zealous.

This fixes CI failure: https://gitlab.gnome.org/GNOME/glib/-/jobs/27125.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
Reviewed-by: nobody

gio/tests/file.c

@@ -153,7 +153,7 @@ typedef struct
   gint monitor_created;
   gint monitor_deleted;
   gint monitor_changed;
-  const gchar *monitor_path;
+  gchar *monitor_path;
   gint pos;
   const gchar *data;
   gchar *buffer;