Include MicrodroidTestPreparer where it's used

This isn't required for local test with atest,
but required for running tests in the cloud with sandboxed environment.

Bug: 277655002, Bug: 272496125
Test: TH
Change-Id: I45551e276a99750340c84ad3c0e5eb7dc2394899
diff --git a/authfs/tests/benchmarks/Android.bp b/authfs/tests/benchmarks/Android.bp
index 38ece79..b30ecdd 100644
--- a/authfs/tests/benchmarks/Android.bp
+++ b/authfs/tests/benchmarks/Android.bp
@@ -24,6 +24,7 @@
         ":CtsApkVerityTestPrebuiltFiles",
         ":MicrodroidTestApp",
     ],
+    required: ["MicrodroidTestPreparer"],
 }
 
 cc_binary {