message: Refactor deposit test to reduce selector noise
diff: @datetime={{postable.timestamp}}
  @imgURL={{postable.author.imgURL}}
  @hideMeta={{postable-meta-identical postable (object-at milestone.visiblePostables (dec j))}}
  - data-test-thread-message={{j}} data-test-milestone={{i}}
  + data-test-postable={{j}} data-test-milestone={{i}}
  >
  {{format-workflow-message postable.message}}
  </Boxel::ThreadMessage>
  @datetime={{postable.timestamp}}
  @imgURL={{postable.author.imgURL}}
  @hideMeta={{postable-meta-identical postable (object-at milestone.visiblePostables (dec j))}}
  - data-test-thread-message={{j}} data-test-milestone={{i}}
  + data-test-postable={{j}} data-test-milestone={{i}}
  >
  {{component postable.componentName onComplete=(optional postable.onComplete)}}
  </Boxel::ThreadMessage>
  