Fix multiple first-time-contributor thank you

[hipstersmoothie]

What Changed

Use the listContributors endpoint to determine who has contributed to the repo.

Why

Fix a bug where a contributor was thanked multiple times in the changelog.

Todo:

• Add tests

Published PR with canary version: 7.12.7-canary.660.8528.0

[codecov]

Codecov Report

Merging #660 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #660      +/-   ##
==========================================
+ Coverage   88.32%   88.33%   +0.01%     
==========================================
  Files          38       38              
  Lines        2124     2126       +2     
  Branches      268      245      -23     
==========================================
+ Hits         1876     1878       +2     
  Misses        214      214              
  Partials       34       34

Impacted Files	Coverage Δ
plugins/first-time-contributor/src/index.ts	100% <100%> (ø)	⬆️

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[adierkens]

🚀 PR was released in v7.12.8 🚀