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.

(Apologies for the additional auto-formatting that removed trailing whitespace!)

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:mag: Inspect the changes: https://github.com/datacarpentry/spreadsheets-socialsci/compare/md-outputs..md-outputs-PR-172

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:stopwatch: Updated at 2023-08-29 13:28:24 +0000

[josenino95]

I confirmed the links one more time and they looked good. Thank you, @froggleston