[MLIR] [Python] Added a missing cast to `__repr__` in the adaptors (#182867)

Without it the return type is inferred as `nanobind::object` which
results in invalid type stubs, since `__repr__` must return `str`.

mlir/include/mlir/Bindings/Python/NanobindAdaptors.h

diff --git a/mlir/include/mlir/Bindings/Python/NanobindAdaptors.h b/mlir/include/mlir/Bindings/Python/NanobindAdaptors.h
index 9180308..9b54baa 100644
--- a/mlir/include/mlir/Bindings/Python/NanobindAdaptors.h
+++ b/mlir/include/mlir/Bindings/Python/NanobindAdaptors.h
@@ -570,8 +570,9 @@
         [isaFunction](MlirAttribute other) { return isaFunction(other); },
         nanobind::arg("other_attribute"), nanobind::sig(kIsinstanceSig));
     def("__repr__", [superCls, captureTypeName](nanobind::object self) {
-      return nanobind::repr(superCls(self))
-          .attr("replace")(superCls.attr("__name__"), captureTypeName);
+      return nanobind::cast<std::string>(
+          nanobind::repr(superCls(self))
+              .attr("replace")(superCls.attr("__name__"), captureTypeName));
     });
     if (getTypeIDFunction) {
       def_staticmethod(