Fix gcc warning about shadowing base class virtual overload.

Adapted from #1048.

PiperOrigin-RevId: 693382358

Author: jnthntatum

eval/public/containers/internal_field_backed_map_impl.h

@@ -45,6 +45,9 @@ class FieldBackedMapImpl : public CelMap {
 
   absl::StatusOr<const CelList*> ListKeys() const override;
 
+  // Suppress warnings about shadowing the base class overload.
+  using CelMap::ListKeys;
+
  protected:
   // These methods are exposed as protected methods for testing purposes since
   // whether one or the other is used depends on build time flags, but each