### Elasticsearch Version

8.9.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

any

### Problem Description

If the context text supplied to the Question Answering task is longer than the model's `max_sequence_length` and `truncate` is set to `none` then inference on the model fails with the message:

```
status_exception: question answering result has invalid dimension, expected 2 found [6] 
```
<img width="1438" alt="Screenshot 2023-07-25 at 08 21 37" src="https://github.com/elastic/elasticsearch/assets/2353640/12d296f6-03b2-4cda-89ce-7399348c4104">


### Steps to Reproduce

Use long input text to the question answering task


### Work Aroundf
The fix is to truncate the context which unfortunately may remove the part of the document containing the answer. For reference the call is documented here

```
POST _ml/trained_models/distilbert-base-cased-distilled-squad/deployment/_infer
{
  "docs":[{ "text_field": "question answering context"}],
  "inference_config": {
    "question_answering": {
      "question": "The question to ask",
      "tokenization": {
        "bert": {
          "truncate": "second",
          "span": -1          
        }
      }
    }
  }
}
````

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/QuestionAnsweringProcessor.java
* @param numAnswersToGather How many top answers to return
     * @param topScoresCollector Called when a score is collected. May be called many more times than numAnswersToGather
     * @param seq2Start The token position of where the context sequence starts. This is AFTER the sequence separation special tokens.
     * @param tokenSize The true total tokenization size. This should NOT include padded tokens.
     * @param maxAnswerLength The maximum answer length to consider.
     * @param spanIndex Which sequence span is this.
     */
    static void topScores(
        double[] start,
        double[] end,
        int numAnswersToGather,
        Consumer<ScoreAndIndices> topScoresCollector,
        int seq2Start,
        int tokenSize,
        int maxAnswerLength,
        int spanIndex
    ) {
        if (start.length != end.length) {
            throw new ElasticsearchStatusException(
                "question answering result has invalid dimensions; possible start tokens [{}] must equal possible end tokens [{}]",
                RestStatus.INTERNAL_SERVER_ERROR,
                start.length,
                end.length
            );
        }