bootclasspath_fragment: Add contents to snapshot

Bug: 177892522
Test: m nothing
Change-Id: I54fe0537b758a0e3dacd34b139ef3eb21b8841fd
diff --git a/apex/testing.go b/apex/testing.go
index 926125f..69bd73e 100644
--- a/apex/testing.go
+++ b/apex/testing.go
@@ -25,5 +25,7 @@
 		// Needed by apex.
 		"system/core/rootdir/etc/public.libraries.android.txt": nil,
 		"build/soong/scripts/gen_ndk_backedby_apex.sh":         nil,
+		// Needed by prebuilt_apex.
+		"build/soong/scripts/unpack-prebuilt-apex.sh": nil,
 	}.AddToFixture(),
 )