Wrong return schema for `engine_getBlobsV2`

[HNYuuu]

In Osaka, engine_getBlobsV2 was introduced. According to its specification (https://github.com/ethereum/execution-apis/blob/main/src/engine/osaka.md#engine_getblobsv2), the return is:

Array of BlobAndProofV2 or null in case of any missing blobs.

However, in the yaml file (https://github.com/ethereum/execution-apis/blob/main/src/engine/openrpc/methods/blob.yaml#L50), the return value is not stricly defined.

I recommend revising it as:

    schema:
      oneOf:
        - type: array
          items:
            - $ref: '#/components/schemas/BlobAndProofV2'
        - type: 'null'

In this way, the yaml file could perfectly reflect the specifications defined in the markdown file.