Fix flag declaration

Metadata block was erroneously removed in a previous CL

Bug: 342366185
Change-Id: I52bec1cbe0583fd589a7aa603a5c2530dbfd914f
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 163c849..780a099 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -964,6 +964,9 @@
   namespace: "systemui"
   description: "Only dismiss media notifications when the control was removed by the user."
   bug: "335875159"
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
 }
 
 flag {