Invalid schema for diff.layout_plugins

Problem/Motivation

When running translation extractions, we're running in to a

 throw new \InvalidArgumentException("Invalid element data for mapping of '$schema_prefix' for '$key'.");

in this case for:

Invalid element data for mapping of 'diff.layout_plugins' for 'type'.

Proposed resolution

It seems to be a minor issue in the schema file for

diff.layout_plugins:
  type: config_object
  label: 'Plugin'
  mapping:
    type: sequence
    sequence:
      type: mapping
      label: 'Diff configuration for a field type'
      mapping:
        type:
          type: text
          label: 'Plugin key'
        settings:
          type: diff.layout_plugin.settings.[%parent.type]

where the mapping should have a fields key (similar to diff.plugins)