fix(rpc): make data field in EthCallMessage optional

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

Reference issue to close (if applicable)

Closes #5352

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[hanabi1224]

if msg.To == builtintypes.EthereumAddressManagerActorAddr {
		return ethtypes.EthBytes{}, nil
	} else if len(invokeResult.MsgRct.Return) > 0 {
		return cbg.ReadByteArray(bytes.NewReader(invokeResult.MsgRct.Return), uint64(len(invokeResult.MsgRct.Return)))
	}

	return ethtypes.EthBytes{}, nil

[LesnyRumcajs]

changelog entry?

[hanabi1224]

changelog entry?

@LesnyRumcajs added.

[LesnyRumcajs]

This isn't helpful to the changelog reader - it's an implementation detail. What would be beneficial is mentioning the RPC methods affected by this change.

[hanabi1224]

Done.