[gnome-builder] gui: fix mismatched gslice usage

[Christian Hergert <chergert src gnome org>]

commit 6b60a5cefe8b2a3782a2e11ffb5d59005f9a73e3
Author: Christian Hergert <chergert redhat com>
Date:   Thu Sep 9 10:57:55 2021 -0700

    gui: fix mismatched gslice usage
    
    Found by Vanadiae
    
    Fixes #1528

 src/libide/gui/ide-session.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/libide/gui/ide-session.c b/src/libide/gui/ide-session.c
index e81888cb9..d0de4f1a0 100644
--- a/src/libide/gui/ide-session.c
+++ b/src/libide/gui/ide-session.c
@@ -934,7 +934,8 @@ on_session_addin_page_saved_cb (GObject      *object,
 
       g_variant_builder_add_value (&s->pages_state, g_variant_dict_end (&state_dict));
     }
-  g_free (save_page);
+
+  g_slice_free (SavePage, save_page);
 
   s->active--;