Bump ImageSharp version

[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

Bump ImageSharp 2.1.3 to include latest jpeg color detection fixes.

[codecov]

Codecov Report

Merging #280 (9185aa7) into main (e10c8a0) will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##           main   #280   +/-   ##
===================================
  Coverage    85%    85%           
===================================
  Files        75     75           
  Lines      2045   2045           
  Branches    298    298           
===================================
  Hits       1741   1741           
  Misses      219    219           
  Partials     85     85           

Flag	Coverage Δ
unittests	85% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e10c8a0...9185aa7. Read the comment docs.

[JimBobSquarePants]

Just gonna merge this and do a release. There's no risk here.