Update to match latest ImageSharp build

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

• API Update to match new Color and ParallelRowIterator APIs
• Update CI to separate Publish from Build and fix Code Coverage.

[codecov]

Codecov Report

Merging #27 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
- Coverage   68.47%   68.44%   -0.03%     
==========================================
  Files          66       66              
  Lines        4951     4941      -10     
==========================================
- Hits         3390     3382       -8     
+ Misses       1561     1559       -2

Flag	Coverage Δ
#unittests	68.44% <100%> (-0.03%)	⬇️

Impacted Files	Coverage Δ
src/ImageSharp.Drawing/Processing/SolidBrush.cs	95% <100%> (ø)	⬆️
...essing/Processors/Drawing/FillProcessor{TPixel}.cs	100% <100%> (+3.22%)	⬆️
src/ImageSharp.Drawing/Processing/RecolorBrush.cs	100% <100%> (ø)	⬆️
src/ImageSharp.Drawing/Processing/PatternBrush.cs	85.71% <100%> (ø)	⬆️
.../Processors/Drawing/FillRegionProcessor{TPixel}.cs	96.51% <100%> (+0.04%)	⬆️
...ImageSharp.Drawing/Processing/PathGradientBrush.cs	91% <100%> (ø)	⬆️
src/ImageSharp.Drawing/Processing/ImageBrush.cs	91.66% <100%> (+0.17%)	⬆️
...c/ImageSharp.Drawing/Processing/BrushApplicator.cs	87.5% <100%> (ø)	⬆️

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