Change keyguard_ondrawn_callback to bugfix flag

Bug: 295873557
Change-Id: Ie12dd70af13c6def70cedc8bd20f771789961c4c
Test: None
Flag: ACONFIG enable_background_keyguard_ondrawn_callback STAGING
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 6e4a4ea..2ad7192 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -168,6 +168,9 @@
         "Note that, even after this callback is called, we're waiting for all windows to finish "
         " drawing."
     bug: "295873557"
+    metadata {
+        purpose: PURPOSE_BUGFIX
+    }
 }
 
 flag {