What type of PR is this?

Other

What does this PR do? Why is it needed?

When unmarshaling a block with fastssz, if the target block's ExecutionRequests field is nil, it will not get populated

if b.ExecutionRequests == nil {
	b.ExecutionRequests = new(v1.ExecutionRequests)
}
if err = b.ExecutionRequests.UnmarshalSSZ(buf); err != nil {
	return err
}

This is true for other fields and that's why we initialize them in our gossip data maps. There is no bug at the moment because even if execution requests are nil, we initialize them in consensus-types/blocks/proto.go

er := pb.ExecutionRequests
if er == nil {
	er = &enginev1.ExecutionRequests{}
}

However, since we initialize other fields in the data map, it's safer to do it for execution requests too, to avoid a bug in case the code in consensus-types/blocks/proto.go changes in the future.

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description to this PR with sufficient context for reviewers to understand this PR.