Fix DF benchmark pushdown options

`predicate_pushdown` is assigned twice; the second should be `projection_pushdown`.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: mprammer <martin@spiraldb.com>

Author: mprammer

benchmarks/datafusion-bench/src/lib.rs

@@ -122,7 +122,7 @@ fn vortex_table_options() -> VortexTableOptions {
     let mut opts = VortexTableOptions::default();
 
     opts.predicate_pushdown = true;
-    opts.predicate_pushdown = true;
+    opts.projection_pushdown = true;
 
     opts
 }