Adjust gitcoin bot get_notifications to use pygithub

[mbeacom]

Description

The goal of this PR is to resolve #1976 and make use of pygithub versus using requests for gathering github notifications.

Checklist

• linter status: 100% pass
• changes don't break existing behavior
• commit message follows commit guidelines

Affected core subsystem(s)

notifications

Testing

Locally

Refers/Fixes

Fixes #1976

[codecov]

Codecov Report

Merging #1977 into master will decrease coverage by <.01%.
The diff coverage is 10%.

@@            Coverage Diff            @@
##           master   #1977      +/-   ##
=========================================
- Coverage    27.8%   27.8%   -0.01%     
=========================================
  Files         137     137              
  Lines       11178   11182       +4     
  Branches     1510    1510              
=========================================
+ Hits         3108    3109       +1     
- Misses       7960    7963       +3     
  Partials      110     110

Impacted Files	Coverage Δ
...itcoinbot/management/commands/get_notifications.py	0% <0%> (ø)	⬆️
app/git/utils.py	46.89% <20%> (-0.43%)	⬇️

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