Treat system_ext as system container

Bug: b/365135457
Test: m
Change-Id: Ic8fd60c0e1045f190b6608931ca1d65a784026f0
diff --git a/aconfig/codegen/java_aconfig_library_test.go b/aconfig/codegen/java_aconfig_library_test.go
index 87b54a4..d8372f3 100644
--- a/aconfig/codegen/java_aconfig_library_test.go
+++ b/aconfig/codegen/java_aconfig_library_test.go
@@ -260,7 +260,7 @@
 			aconfig_declarations {
 				name: "my_aconfig_declarations_bar",
 				package: "com.example.package.bar",
-				container: "system_ext",
+				container: "vendor",
 				srcs: ["bar.aconfig"],
 			}