Update scalafmt-core to 3.9.4 (#348)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: scala-steward

.scalafmt.conf

@@ -1,2 +1,2 @@
-version = "3.9.3"
+version = "3.9.4"
 runner.dialect="scala213source3"