Truncate slack block text so it is not rejected by slack API

[mderynck]

What this PR does

Truncates text for slack message to avoid this error:

File "/usr/local/lib/python3.12/site-packages/slack_sdk/web/slack_response.py", line 199, in validate
    raise e.SlackApiError(message=msg, response=self)
slack_sdk.errors.SlackApiError: The request to the Slack API failed. (url: https://www.slack.com/api/chat.postMessage)
The server responded with: {'ok': False, 'error': 'invalid_blocks', 'errors': ['failed to match all allowed schemas [json-pointer:/blocks/0/text]', 'must be less than 3001 characters [json-pointer:/blocks/0/text/text]'], 'response_metadata': {'messages': ['[ERROR] failed to match all allowed schemas [json-pointer:/blocks/0/text]', '[ERROR] must be less than 3001 characters [json-pointer:/blocks/0/text/text]']}}

Which issue(s) this PR closes

Related to [issue link here]

Checklist

• Unit, integration, and e2e (if applicable) tests updated
• Documentation added (or pr:no public docs PR label added if not required)
• Added the relevant release notes label (see labels prefixed w/ release:). These labels dictate how your PR will
  show up in the autogenerated release notes.