Replace reference to defunct Google Group with opening a GitHub Issue

[n2ygk]

Fixes: #924

Description of the Change

Replace documentation reference to defunct Google Group with instructions to open an issue.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #942 (fb8380d) into master (b56987e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #942   +/-   ##
=======================================
  Coverage   96.59%   96.59%           
=======================================
  Files          31       31           
  Lines        1704     1704           
=======================================
  Hits         1646     1646           
  Misses         58       58           

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[n2ygk]

I've requested enabling GitHub Discussions at which point we can change this to point there instead.

[amureki]

Tested the link, it works!

Thank you for the fix 👍