Bump ImageSharp

[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

Bumps ImageSharp to v2.1.5 to include latest security fixes.

Also adds publishing to the build pipeline.

[codecov]

Codecov Report

Merging #285 (5da0c8f) into main (7b2a1ce) will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##           main   #285   +/-   ##
===================================
  Coverage    80%    80%           
===================================
  Files        97     97           
  Lines      5024   5024           
  Branches    919    919           
===================================
  Hits       4029   4029           
  Misses      796    796           
  Partials    199    199           

Flag	Coverage Δ
unittests	80% <ø> (ø)

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