Add VM creation failure test for unsigned vendor image

Bug: 285855436
Test: atest MicrodroidTests#creationFailsWithUnsignedVendorPartition

Change-Id: I1a8ec9d08a12a05fabb67a776e47eeeb24cf23be
diff --git a/tests/vendor_images/Android.bp b/tests/vendor_images/Android.bp
index e5f863a..f065b5c 100644
--- a/tests/vendor_images/Android.bp
+++ b/tests/vendor_images/Android.bp
@@ -15,3 +15,9 @@
     use_avb: true,
     avb_private_key: ":vendor_sign_key",
 }
+
+android_filesystem {
+    name: "test_microdroid_vendor_image_unsigned",
+    type: "ext4",
+    file_contexts: ":microdroid_vendor_file_contexts.gen",
+}