Bold italic via markdown does not terminate bold as expected

[benjie]

Summary

After entering _**Bold italic**_ into editor, when you continue typing text is still bold.

Steps to reproduce

1. Enter the below into remirror playground
2. Type the following characters at the end of the editor: **_ more words

{
  "doc": {
    "type": "doc",
    "content": [
      {
        "type": "paragraph",
        "content": [
          {
            "type": "text",
            "text": "Here's _**bold italic"
          }
        ]
      }
    ]
  },
  "playground": {
    "m": 0,
    "a": [],
    "e": [
      {
        "module": "remirror/extension/bold",
        "export": "BoldExtension"
      },
      {
        "module": "remirror/extension/italic",
        "export": "ItalicExtension"
      }
    ],
    "p": []
  }
}

Expected results

Bold italic more words

Actual results

Bold italic more words

[ifiokjr]

What a great format for this issue. It took me less than 2 minutes to verify the bug and once a fix is available it'll also be verifiable via the playground. Love it 😊