Update drawing tests to use new renderer

[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

Updates the unit tests to use the new canvas-based API from ImageSharp.Drawing for the render tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84%. Comparing base (4bbe910) to head (fdc3602).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #531   +/-   ##
=====================================
  Coverage     84%     84%           
=====================================
  Files        332     332           
  Lines      24634   24634           
  Branches    3609    3609           
=====================================
  Hits       20737   20737           
  Misses      3010    3010           
  Partials     887     887           

Flag	Coverage Δ
unittests	84% <100%> (ø)

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