Rust: Fix unused import warning in RustOnly test

Tests/RustOnly/main.rs

diff --git a/Tests/RustOnly/main.rs b/Tests/RustOnly/main.rs
index d177874..af91fc3 100644
--- a/Tests/RustOnly/main.rs
+++ b/Tests/RustOnly/main.rs
@@ -17,5 +17,6 @@
     unsafe { liba_greet() };
     unsafe { libb_greet() };
     libc_greet();
+    libd_greet();
     unsafe { libe_greet() };
 }