Update sbt-scalafmt to 2.3.1

[scala-steward]

Updates org.scalameta:sbt-scalafmt from 2.3.0 to 2.3.1.
Release Notes/Changelog

I'll automatically update this PR to resolve conflicts as long as you don't change it yourself.

If you'd like to skip this version, you can just close this PR. If you have any feedback, just mention me in the comments below.

Have a fantastic day writing Scala!

Ignore future updates

Add this to your .scala-steward.conf file to ignore future updates of this dependency:

updates.ignore = [ { groupId = "org.scalameta", artifactId = "sbt-scalafmt" } ]

labels: sbt-plugin-update, semver-patch

[codecov-io]

Codecov Report

Merging #3277 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3277   +/-   ##
=======================================
  Coverage   93.17%   93.17%           
=======================================
  Files         378      378           
  Lines        7573     7573           
  Branches      197      197           
=======================================
  Hits         7056     7056           
  Misses        517      517

Flag	Coverage Δ
#scala_version_212	93.39% <ø> (-0.03%)	⬇️
#scala_version_213	92.94% <ø> (-0.02%)	⬇️

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