It should be possible to ignore the result of QTaskBuilder::spawn

QTaskBuilder::spawn marked as [[nodiscard]], but it might be required to ignore a future object returned from this function. In this case, it should be explicitly declared. There are a few ways of implementation:

1) Add explicit function named like "ignoreResult" to the builder class

2) Add a tag (e.g. IgnoreResult) to the spawn function call

Ideally, a separate function specialization that returns void should be implemented.