[PDL] fix unused variable warning in Release builds

GitOrigin-RevId: 1b0312d2809701dd766dd3705b460362653bffcf
diff --git a/lib/Conversion/PDLToPDLInterp/PredicateTree.cpp b/lib/Conversion/PDLToPDLInterp/PredicateTree.cpp
index eef8f3a..2466a80 100644
--- a/lib/Conversion/PDLToPDLInterp/PredicateTree.cpp
+++ b/lib/Conversion/PDLToPDLInterp/PredicateTree.cpp
@@ -491,6 +491,7 @@
         // cheaper to start the traversal at this value rather than at the
         // `connector`, violating the optimality of our spanning tree.
         bool inserted = valueToPosition.try_emplace(value, opPos).second;
+        (void)inserted;
         assert(inserted && "duplicate upward visit");
 
         // Obtain the tree predicates at the current value.