libgui: Make bq_gl_fence_cleanup a bugfix flag

Bug: 339705065
Flag: EXEMPT flagging
Test: n/a
Change-Id: If44ca64cc6f97629b594a2ea1deea36c66923175
diff --git a/libs/gui/libgui_flags.aconfig b/libs/gui/libgui_flags.aconfig
index 6bf38c0..394a5cf 100644
--- a/libs/gui/libgui_flags.aconfig
+++ b/libs/gui/libgui_flags.aconfig
@@ -138,4 +138,7 @@
   description: "Remove BufferQueueProducer::dequeue's wait on this fence (or the fence entirely) to prevent deadlocks"
   bug: "339705065"
   is_fixed_read_only: true
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
 } # bq_gl_fence_cleanup