Fix Build Process.

[JimBobSquarePants]

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• I have provided test coverage for my change (where applicable)

Description

There's something funny going on with versioning for .NET Core 3.1. See #137

I've checked and none of our other repositories are affected so I'm assuming (hoping) it's something to do with this repositories git history

Looking at the publish step there's a warning that the project directory is not a valid git folder. I'm going to see if simplifying the process to use standard action options fixes the issue.
https://github.com/SixLabors/ImageSharp.Drawing/runs/2644202851?check_suite_focus=true#step:5:82

[codecov]

Codecov Report

Merging #138 (8aafd9e) into master (eccffe8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #138   +/-   ##
=======================================
  Coverage   69.35%   69.35%           
=======================================
  Files          89       89           
  Lines        5142     5142           
  Branches     1051     1051           
=======================================
  Hits         3566     3566           
  Misses       1359     1359           
  Partials      217      217           

Flag	Coverage Δ
unittests	69.35% <ø> (ø)

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[JimBobSquarePants]

Ok... Versioning on build is correct but the only way to really test this (since I couldn't replicate it locally) is to merge to master and let publish run.