[windows] Remove unused pybind exception params

[NathanielMcVicar]

Summary

Resolve MSVC warning C4104 for unreferenced variable

[NathanielMcVicar]

Fixed reference, I'm not clear why this isn't const, since unlike other pybind exceptions cast_error doesn't appear to be handled by Python.

[NathanielMcVicar]

clang-format

mlir/lib/Bindings/Python/IRInterfaces.cpp

 public:
   /// Constructs an interface instance from an object that is either an
   /// operation or a subclass of OpView. In the latter case, only the static
   /// methods of the interface are accessible to the caller.
   PyConcreteOpInterface(py::object object, DefaultingPyMlirContext context)
       : obj(std::move(object)) {
     try {
       operation = &py::cast<PyOperation &>(obj);
-    } catch (py::cast_error &err) {
+    } catch (py::cast_error) {
       // Do nothing.
     }
 
     try {
       operation = &py::cast<PyOpView &>(obj).getOperation();
-    } catch (py::cast_error &err) {
+    } catch (py::cast_error) {
       // Do nothing.
     }
 
     if (operation != nullptr) {
       if (!mlirOperationImplementsInterface(*operation,
                                             ConcreteIface::getInterfaceID())) {
         std::string msg = "the operation does not implement ";
         throw py::value_error(msg + ConcreteIface::pyClassName);
       }
 
       MlirIdentifier identifier = mlirOperationGetName(*operation);
       MlirStringRef stringRef = mlirIdentifierStr(identifier);
       opName = std::string(stringRef.data, stringRef.length);
     } else {
       try {
         opName = obj.attr("OPERATION_NAME").template cast<std::string>();
-      } catch (py::cast_error &err) {
+      } catch (py::cast_error) {
         throw py::type_error(
             "Op interface does not refer to an operation or OpView class");
       }
 
       if (!mlirOperationImplementsInterfaceStatic(
               mlirStringRefCreate(opName.data(), opName.length()),
               context.resolve().get(), ConcreteIface::getInterfaceID())) {
         std::string msg = "the operation does not implement ";