Add missing aconfig container field to frameworks/opt/telephony

Bug: 330354107
Test: CI

Flag: NONE

Ignore-AOSP-First: It is easier to detect all the mismatch in internal
master.

Change-Id: Iacfa9252ccfde7743f54d35b88405253ed78c91d
diff --git a/flags/subscription.aconfig b/flags/subscription.aconfig
index 5bc5340..60c0af1 100644
--- a/flags/subscription.aconfig
+++ b/flags/subscription.aconfig
@@ -1,4 +1,5 @@
 package: "com.android.internal.telephony.flags"
+container: "system"
 
 # OWNER=linggm TARGET=24Q3
 flag {