Update scala-library to 2.12.21 (#311)

Author: scala-steward

build.sbt

@@ -46,7 +46,7 @@ lazy val types = crossProject(JSPlatform, JVMPlatform)
   .crossType(CrossType.Pure)
   .settings(commonSettings)
   .settings(
-    crossScalaVersions := Seq("2.12.20", "2.13.16", "3.3.0"),
+    crossScalaVersions := Seq("2.12.21", "2.13.16", "3.3.0"),
     name := "sloth-types",
     libraryDependencies ++=
       Deps.cats.value ::