minor renaming

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: timsaucer

datafusion/ffi/src/execution_plan.rs

@@ -152,7 +152,7 @@ unsafe extern "C" fn execute_fn_wrapper(
     let runtime = plan.runtime();
     let plan = plan.inner();
 
-    let _guard = runtime.as_ref().map(|rt| rt.enter());
+    let _runtime_guard = runtime.as_ref().map(|rt| rt.enter());
 
     rresult!(
         plan.execute(partition, ctx)