docs: fix community call calendar link, slack instructions

[jescalada]

Provides instructions on how to get the Community Call recurring meeting invite (which can be done via the same meeting link).

Description

Fixes the broken invite links.

Checklist

General

• I have read the CONTRIBUTING.md guidelines
• Commit messages follow Conventional Commits format
• I have a FINOS CLA on file

[netlify]

✅ Deploy Preview for endearing-brigadeiros-63f9d0 canceled.

Name	Link
🔨 Latest commit	38a445d
🔍 Latest deploy log	https://app.netlify.com/projects/endearing-brigadeiros-63f9d0/deploys/6a14f40e63cca900087a4bbc

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.10%. Comparing base (a60e51a) to head (38a445d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1546   +/-   ##
=======================================
  Coverage   90.10%   90.10%           
=======================================
  Files          69       69           
  Lines        5657     5657           
  Branches      990      990           
=======================================
  Hits         5097     5097           
  Misses        541      541           
  Partials       19       19           

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