Possibly missing field "user" in message_changed event

[siketyan]

After upgrading from 1.14.5 to 1.16.0, we are experiencing an error:

Slack listener error occurred: SlackClientProtocolError { json_error: Error("missing field `user`", line: 0, column: 0), json_body: Some(...)

It seems slack-morphism-rust expects SlackMessageEventEdited::user is not optional, but actually it is omitted when the message was edited by a bot.

Related PR: #226

This is an example of the payload which occur the error:

{
  "token": "[REDACTED]",
  "team_id": "[REDACTED]",
  "enterprise_id": "[REDACTED]",
  "context_team_id": "[REDACTED]",
  "context_enterprise_id": "[REDACTED]",
  "api_app_id": "[REDACTED]",
  "event": {
    "type": "message",
    "subtype": "message_changed",
    "message": {
      "type": "message",
      "subtype": "bot_message",
      "text": "[REDACTED]",
      "username": "[REDACTED]",
      "bot_id": "[REDACTED]",
      "app_id": "[REDACTED]",
      "blocks": [
        {
          "type": "section",
          "block_id": "FF1Ng",
          "text": {
            "type": "mrkdwn",
            "text": "[REDACTED]",
            "verbatim": false
          }
        }
      ],
      "edited": {
        "user": "[REDACTED]",
        "ts": "1702549421.000000"
      },
      "ts": "1702549413.998139",
      "source_team": "[REDACTED]",
      "user_team": "[REDACTED]"
    },
    "previous_message": {
      "type": "message",
      "subtype": "bot_message",
      "text": "[REDACTED]",
      "ts": "1702549413.998139",
      "username": "[REDACTED]",
      "bot_id": "[REDACTED]",
      "app_id": "[REDACTED]",
      "blocks": [
        {
          "type": "section",
          "block_id": "jT48G",
          "text": {
            "type": "mrkdwn",
            "text": "[REDACTED]",
            "verbatim": false
          }
        }
      ]
    },
    "channel": "[REDACTED]",
    "hidden": true,
    "ts": "1702549421.000900",
    "event_ts": "1702549421.000900",
    "channel_type": "channel"
  },
  "type": "event_callback",
  "event_id": "[REDACTED]",
  "event_time": 1702549421,
  "authorizations": [
    {
      "enterprise_id": "[REDACTED]",
      "team_id": "[REDACTED]",
      "user_id": "[REDACTED]",
      "is_bot": false,
      "is_enterprise_install": false
    }
  ],
  "is_ext_shared_channel": false,
  "event_context": "[REDACTED]"
}

[abdolence]

Hey, damn, sorry - I missed that when I reviewed the changes. Thanks for the fix!

[abdolence]

Released in https://github.com/abdolence/slack-morphism-rust/releases/tag/v1.16.1