Update test: true to mode: "test" in java_aconfig_library

Test: CI

Bug: 309990433
Change-Id: I6c54a4206770ccaba3feec9746d251ca6455228a
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index 5a3bca1..6e6c6d8 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -45,7 +45,7 @@
 cc_aconfig_library {
     name: "libsurfaceflingerflags_test",
     aconfig_declarations: "surfaceflinger_flags",
-    test: true,
+    mode: "test",
 }
 
 cc_test {