Trix no longer adds dataset attributes on inserted attachments in 2.1.4

Describe the bug or issue here…

##### Steps to Reproduce

1. Go to https://trix-editor.org/
2. Delete all of the content
3. Paste the following code into the console and run it
```js
(() => {
const trix = document.querySelector("trix-editor");
const attachment = new Trix.Attachment({
"attachment-type": "custom",
"content": "

",
"contentType": "custom"
});

trix.editor.insertAttachment(attachment)
})()
```
4. Inspect the attachment within Trix and see that the div element is missing the data-item-id attribute

This was working fine prior to version 2.1.4.

##### Details

* Trix version: 2.1.4
* Browser name and version: Chrome 127.0.6533.89 (Official Build) (arm64)
* Operating system: MacOS

Start by reproducing the attachment insertion through Trix.Attachment and trix.editor.insertAttachment on the Trix demo using version 2.1.4. Compare the behavior with a pre-2.1.4 version and trace how the inserted attachment content is handled; the work is done when the div retains its data-item-id attribute.

Written by the indexing model from the issue text.