HarmonyOS List组件Header吸顶时，Header与其上方组件之间会存一条线的在间隙

可以增加 .pixelRound属性，设置向下取整即可。

参考文档：

https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/ts-universal-attributes-layout-constraints-V5#pixelround11

https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/ts-appendix-enums-V5#pixelroundcalcpolicy11

示例Demo代码：

@Entry
@Component
export struct ListHeaderPage {
  array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  @Builder
  Header() {
    Text('Header,可吸顶').size({ width: '100%', height: 30 })
      .backgroundColor('#ff0000')
  }
  build() {
    Column() {
      Text('List上方组件').size({ width: '100%', height: 30 })
        .backgroundColor('#ff0000')
      List() {
        ListItem().backgroundColor('#FFFFFF')
          .size({ width: '100%', height: 30 })
        ListItemGroup({ header: this.Header() }) {
          ForEach(this.array, (value: number) => {
            ListItem(){
              Text('ListItem').size({ width: '100%', height: 50 })
                .backgroundColor('#ffff00')
                .margin({ top: 5 })
            }
          })
        }
        .pixelRound({
          start:PixelRoundCalcPolicy.FORCE_FLOOR,
          top:PixelRoundCalcPolicy.FORCE_FLOOR,
          end: PixelRoundCalcPolicy.FORCE_FLOOR,
          bottom: PixelRoundCalcPolicy.FORCE_FLOOR
        })
      }
      .scrollBar(BarState.Off)
      .sticky(StickyStyle.Header)
      .edgeEffect(EdgeEffect.None)
      .width('100%')
      .height('100%')
    }
    .size({ width: '100%', height: '100%' })
  }
}
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