Let test_microdroid_vendor_image use avb

This change will allow using avb and public key for the vendor partition
verification.

Bug: 285855436
Test: adb shell /apex/com.android.virt/bin/vm run-microdroid --vendor /data/local/tmp/test_microdroid_vendor_image.img
Test: atest MicrodroidTestApp using ABTD

Change-Id: I829b90be4c7f5c4b6c0450b129ab6423f5bfc2b6
diff --git a/tests/vendor_images/Android.bp b/tests/vendor_images/Android.bp
index 09c657c..e5f863a 100644
--- a/tests/vendor_images/Android.bp
+++ b/tests/vendor_images/Android.bp
@@ -2,8 +2,16 @@
     default_applicable_licenses: ["Android-Apache-2.0"],
 }
 
+prebuilt_etc {
+    name: "vendor_sign_key",
+    src: ":avb_testkey_rsa4096",
+    installable: false,
+}
+
 android_filesystem {
     name: "test_microdroid_vendor_image",
     type: "ext4",
     file_contexts: ":microdroid_vendor_file_contexts.gen",
+    use_avb: true,
+    avb_private_key: ":vendor_sign_key",
 }