Update slack links

[froggleston]

The Carpentries recently updated their Slack domain URL and invite app URL. This PR updates the links to match the new domains.

[github-actions]

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🔍 Inspect the changes: https://github.com/datacarpentry/sql-ecology-lesson/compare/md-outputs..md-outputs-PR-365

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⏱️ Updated at 2023-08-29 13:09:56 +0000

[adamancer]

Thanks, @froggleston!