Add media-linker-config to test media APEX

media-linker-config was not added to test media APEX, so test media APEX
was not visible from linker. This change adds media-linker-config to
test media APEX so Media APEX can keep visible from test environment.

Bug: 170592137
Test: media_e2e_tests passed from crosshatch
Change-Id: I29ec401bc019527c762a128daf681f60352434e4
diff --git a/apex/testing/Android.bp b/apex/testing/Android.bp
index a04ab3f..d86094e 100644
--- a/apex/testing/Android.bp
+++ b/apex/testing/Android.bp
@@ -17,7 +17,10 @@
     manifest: "test_manifest.json",
     file_contexts: ":com.android.media-file_contexts",
     defaults: ["com.android.media-defaults"],
-    prebuilts: ["sdkinfo_45"],
+    prebuilts: [
+        "sdkinfo_45",
+        "media-linker-config",
+    ],
     installable: false,
 }