geojson pick confusion when set perPositionHeight

hello

I use GeoJsonDataSource to load geojson data, when i set the perPositionHeight=false,single click on the map to pickup a geojson feathure, it may return a wrong result.


when i set entity.polygon.perPositionHeight = false, it will happen,but if set entity.polygon.perPositionHeight = true, it works fine. this happens with cesium version 1.88, when change cesium version to 1.74,it works fine as well.

following is the code:
```js
var promise = Cesium.GeoJsonDataSource.load('data/wenmiao.json', { clampToGround: true });
promise.then(function (dataSource) {
// viewer.dataSources.add(dataSource);
var entities = dataSource.entities.values;
for (var i = 0; i < entities.length; i++) {
var entity = entities[i];
entity.polygon.perPositionHeight = false;
entity.polygon.classificationType = Cesium.ClassificationType.BOTH;
entity.heightReference = Cesium.HeightReference.CLAMP_TO_GROUND
entity.polygon.material= Cesium.Color.BLUE;
viewer.entities.add(entity)
}
});
viewer.flyTo(promise);
var scene = viewer.scene;

var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
handler.setInputAction(function (movement) {
var pick = viewer.scene.pick(movement.position);
if(pick){
selectedEntity = pick.id;
pick.id.polygon.material = new Cesium.Color(255, 0, 0, 1)
}
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);
```

The report names no repository files or tests; start by running the supplied GeoJsonDataSource and scene.pick reproduction with Cesium 1.88 and perPositionHeight=false. Done means a single click consistently identifies the intended GeoJSON entity, while the reported true and Cesium 1.74 comparisons remain understandable.

Written by the indexing model from the issue text.