Update scala-library, scala-reflect to 2.12.21

Author: scala-steward

build.sbt

@@ -23,7 +23,7 @@ lazy val main = (project in file("."))
     name               := repo,
     description        := "Simple, safe and intuitive I/O in Scala",
     organization       := s"com.github.$username",
-    crossScalaVersions := Seq("2.11.12", "2.12.17", "2.13.10", "3.2.2"),
+    crossScalaVersions := Seq("2.11.12", "2.12.21", "2.13.10", "3.2.2"),
     crossVersion       := CrossVersion.binary,
     scalacOptions      := scalacOptions.value diff rmCompilerFlags(scalaVersion.value),
     Compile / compile  := (Compile / compile).dependsOn(Compile / scalafmt, Test / scalafmt, Compile / scalafmtSbt).value,