[tool] fix: update slack link in CONTRIBUTING.md (#4719)

[guillaumejparis]

Updated Slack channel link to the new community URL.

Proposed changes

Testing Instructions

1. Step-by-step how to test
2. Environment or config notes

Related issues

• Closes Not able to join slack channel through link present in Contribution.md #4719

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality
• For bug fix -> I implemented a test that covers the bug

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.57%. Comparing base (b8c0b6a) to head (25ff36d).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #4721   +/-   ##
=========================================
  Coverage     50.57%   50.57%           
  Complexity     3708     3708           
=========================================
  Files           903      903           
  Lines         26819    26819           
  Branches       2012     2012           
=========================================
  Hits          13563    13563           
  Misses        12437    12437           
  Partials        819      819           

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