Append change method throws error when used on moderation_state field

Problem/Motivation

The "Append to the current value" change method causes a fatal exception when used on the Moderation state field provided by core's Content Moderation.

E.g
The state 'draft published' does not exist in workflow.

Steps to reproduce

Update the moderation state field via a bulk edit action and select "Append to current value"

Proposed resolution

Skip the moderation_state field when checking which options to add. There's most likely other fields we need to skip this for too.