HarmonyOS audioManager监听音量变化无回调

audioManager是局部变量，局部变量出来之后就被析构了。

参考代码：

@State audioManager:audio.AudioManager |null=null
@State audioVolumeManager:audio.AudioVolumeManager | null =null
voiceChangeDemo() {
  console.info('tag', 'aboutToAppear')
  this.audioManager = audio.getAudioManager();
  this.audioVolumeManager = this.audioManager?.getVolumeManager();
  this.audioVolumeManager?.on('volumeChange', (volumeEvent: audio.VolumeEvent) => {
    console.info('tag', `VolumeType of stream: ${volumeEvent.volumeType} `);
    console.info(`Volume level: ${volumeEvent.volume} `);
    console.info(`Whether to updateUI: ${volumeEvent.updateUi} `);
  });
}
aboutToAppear(): void {
  this.voiceChangeDemo()
}