Fix delete_records slack formatting

[stacimc]

Fixes

Description

Very small change to fix the formatting of the reported record_count in the Slack message from the delete_records DAG.

Testing Instructions

Unit test should pass. If you'd like, you can also run the delete_records DAG locally with a conf that will select >=1k records, example:

{
  "reason":"deadlink"
  "select_query":"WHERE provider in ('freesound', 'wikimedia_audio');"
  "table_name":"audio"
}

Then look at the message for the final, notify_slack task and it should be formatted properly (Deleted 4,172 records from the audio table matching query: 'WHERE provider in ('jamendo', 'wikimedia_audio')')

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (if applicable).

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[AetherUnbound]

LGTM!

[dhruvkb]

+1 for @AetherUnbound's suggestion, LGTM!