Update to Python 3.9

[alysivji]

What does this do

Updating to Python 3.9

Why are we doing this

Lots of quality of life improvement in 3.9

How should this be tested

Do tests pass? then we are good

Migrations

n/a

Dependencies

n/a

Callouts

n/a

[codecov-io]

Codecov Report

Merging #335 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #335      +/-   ##
==========================================
+ Coverage   89.83%   89.87%   +0.04%     
==========================================
  Files          71       71              
  Lines        2499     2499              
==========================================
+ Hits         2245     2246       +1     
+ Misses        254      253       -1     

Impacted Files	Coverage Δ
busy_beaver/common/wrappers/slack.py	96.77% <0.00%> (+1.61%)	⬆️

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