Merge pull request #2222 from scala-steward/update/specs2-core-4.21.0

Update specs2-core to 4.21.0

Author: jatcwang

build.sbt

@@ -21,7 +21,7 @@ lazy val scalatestVersion = "3.2.18"
 lazy val munitVersion = "1.1.0"
 lazy val shapelessVersion = "2.3.13"
 lazy val silencerVersion = "1.7.1"
-lazy val specs2Version = "4.20.9"
+lazy val specs2Version = "4.21.0"
 lazy val scala212Version = "2.12.20"
 lazy val scala213Version = "2.13.16"
 lazy val scala3Version = "3.3.5"