Document `RegisterTaskObject` ignoring `allowEarlyCollection`

[rainersigwald]

msbuild/src/Shared/RegisteredTaskObjectCacheBase.cs

Lines 59 to 64 in 8b03742

	public void RegisterTaskObject(object key, object obj, RegisteredTaskObjectLifetime lifetime, bool allowEarlyCollection)
	{
	ConcurrentDictionary<object, object> dict = GetCollectionForLifetime(lifetime, dontCreate: false);
	dict?.TryAdd(key, obj);
	}

Notice how allowEarlyCollection is ignored. It was dropped in some pre-GitHub release. We should document that.