Allow tools/vendor to build rust

This is necessary to move the mk_payload package from
packages/modules/Virtualization/microdroid to an ARC owned directory.

Bug: 196891323
Test: m -j
Change-Id: Ifa3e509fb4ffa7861e45f69dd4654e8fbe1677ff
diff --git a/rust/config/allowed_list.go b/rust/config/allowed_list.go
index 0d0b712..f318507 100644
--- a/rust/config/allowed_list.go
+++ b/rust/config/allowed_list.go
@@ -36,6 +36,7 @@
 		"system/tools/aidl",
 		"tools/security/fuzzing/example_rust_fuzzer",
 		"tools/security/fuzzing/orphans",
+		"tools/vendor",
 		"vendor/",
 	}