Fix `cancelButtonStyle` & `confirmButtonStyle` properties  from `TimePickerTheme`  aren't working (#132843)

fixes [`TimePickerThemeData` action buttons styles aren't working](https://github.com/flutter/flutter/issues/132760)

### Code sample

<details> 
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        useMaterial3: true,
        timePickerTheme: TimePickerThemeData(
          cancelButtonStyle: TextButton.styleFrom(
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(4)),
              side: BorderSide(color: Colors.red),
            ),
            backgroundColor: Colors.white,
            foregroundColor: Colors.red,
            elevation: 3,
            shadowColor: Colors.red,
          ),
          confirmButtonStyle: TextButton.styleFrom(
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(4)),
            ),
            backgroundColor: Colors.green[700],
            foregroundColor: Colors.white,
            elevation: 3,
            shadowColor: Colors.green[700],
          ),
        ),
      ),
      home: const Example(),
    );
  }
}

class Example extends StatelessWidget {
  const Example({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TimePickerDialog(initialTime: TimeOfDay.now()),
      ),
    );
  }
}

``` 

</details>

### Before (action buttons don't use the style from the `TimePickerTheme`)

![Screenshot 2023-08-18 at 14 57 37](https://github.com/flutter/flutter/assets/48603081/c95160e2-76a2-4bb5-84e0-3731fce19c0b)

### After (action buttons use the style from the `TimePickerTheme`)

![Screenshot 2023-08-18 at 14 57 18](https://github.com/flutter/flutter/assets/48603081/422d348a-bee2-4696-8d9a-5fce56191aaa)