Update scalafmt-core to 3.9.4 (scalapb#308)

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"