Revert "[mlir][python] disable nanobind leak warnings (llvm#121099)"

This reverts commit 08e2c15.

Author: MaheshRavishankar

mlir/lib/Bindings/Python/IRCore.cpp

@@ -2593,8 +2593,6 @@ class PyOpAttributeMap {
 //------------------------------------------------------------------------------
 
 void mlir::python::populateIRCore(nb::module_ &m) {
-  // disable leak warnings which tend to be false positives.
-  nb::set_leak_warnings(false);
   //----------------------------------------------------------------------------
   // Enums.
   //----------------------------------------------------------------------------