res_ari: fix memory leak for channelvars

In ari.conf, when setting the option channelvars, every Stasis channel
snapshot would create a list of variable/value that would not be freed
when the snapshot is freed, resulting in a often-recurring memory
leak.

ASTERISK-26767 #close

Change-Id: Ia37dd9d68063d7f879193df02ede293e5ded716d

main/stasis_channels.c

@@ -197,6 +197,7 @@ static void channel_snapshot_dtor(void *obj)
 
 	ast_string_field_free_memory(snapshot);
 	ao2_cleanup(snapshot->manager_vars);
+	ao2_cleanup(snapshot->ari_vars);
 }
 
 struct ast_channel_snapshot *ast_channel_snapshot_create(struct ast_channel *chan)