Update scalafmt-core to 2.6.4

[scala-steward]

Updates org.scalameta:scalafmt-core from 2.6.3 to 2.6.4.
GitHub Release Notes - Version Diff

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

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Ignore future updates

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

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

labels: library-update, semver-patch

[codecov-commenter]

Codecov Report

Merging #3525 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3525   +/-   ##
=======================================
  Coverage   91.33%   91.33%           
=======================================
  Files         386      386           
  Lines        8588     8588           
  Branches      252      267   +15     
=======================================
  Hits         7844     7844           
  Misses        744      744