Bump Scala 2.12 to 2.12.21

modules/directives/src/main/scala/scala/build/preprocessing/directives/Plugin.scala

@@ -11,7 +11,7 @@ import scala.build.preprocessing.directives.DirectiveUtil.*
 import scala.cli.commands.SpecificationLevel
 
 @DirectiveGroupName("Compiler plugins")
-@DirectiveExamples("//> using plugin org.typelevel:::kind-projector:0.13.2")
+@DirectiveExamples("//> using plugin org.typelevel:::kind-projector:0.13.4")
 @DirectiveUsage(
   "//> using plugin org:name:ver | //> using plugins org:name:ver org2:name2:ver2",
   "`using plugin` _org_`:`_name_`:`_ver_"

modules/integration/src/test/scala/scala/cli/integration/CompileTests212.scala

@@ -15,7 +15,7 @@ class CompileTests212 extends CompileTestDefinitions with Test212 {
         |""".stripMargin
   )
 
-  val kindProjectPlugin = "org.typelevel:::kind-projector:0.13.3"
+  val kindProjectPlugin = "org.typelevel:::kind-projector:0.13.4"
 
   test("should compile with compiler plugin") {
     pluginInputs.fromRoot { root =>

project/deps/package.mill.scala

@@ -11,7 +11,7 @@ object Cli {
 }
 
 object Scala {
-  def scala212            = "2.12.20"
+  def scala212            = "2.12.21"
   def scala213            = "2.13.18"
   def scala3LtsPrefix     = "3.3"                  // used for the LTS version tags
   def scala3Lts           = s"$scala3LtsPrefix.7"  // the LTS version currently used in the build

website/docs/cookbooks/introduction/scala-versions.md

@@ -106,15 +106,15 @@ scala-cli ScalaVersion.scala version.scala
 Scala: 2\.12\.
 -->
 
-The output at the time of this writing is "`2.12.18`".
+The output at the time of this writing is "`2.12.21`".
 
 The Scala CLI philosophy is “command line first,” so any configuration information that’s passed to the command line will override `using` directives. So when you run this command with the `-S` option:
 
 ```bash
 scala-cli -S 2.13.15 ScalaVersion.scala version.scala
 ```
 
-the result is "`2.13.15`" (as opposed to "`2.12.18`" in the previous example).
+the result is "`2.13.15`" (as opposed to "`2.12.21`" in the previous example).
 
 <!-- Expected-regex:
 Scala: 2\.13\.15

website/docs/reference/directives.md

@@ -67,7 +67,7 @@ Adds compiler plugins
 `using plugin` _org_`:`_name_`:`_ver_
 
 #### Examples
-`//> using plugin org.typelevel:::kind-projector:0.13.2`
+`//> using plugin org.typelevel:::kind-projector:0.13.4`
 
 ### Compute Version
 

website/docs/reference/scala-command/directives.md

@@ -49,7 +49,7 @@ Adds compiler plugins
 `using plugin` _org_`:`_name_`:`_ver_
 
 #### Examples
-`//> using plugin org.typelevel:::kind-projector:0.13.2`
+`//> using plugin org.typelevel:::kind-projector:0.13.4`
 
 ### Dependency
 

website/docs/reference/scala-versions.md

@@ -35,5 +35,5 @@ it is recommended to update scala-cli.
 | 1.8.5 - 1.9.0      |  3.7.2  |    2.13.16 |    2.12.20 |
 | 1.9.1              |  3.7.3  |    2.13.16 |    2.12.20 |
 | 1.10.0 - 1.10.1    |  3.7.4  |    2.13.17 |    2.12.20 |
-| 1.10.2 - current   |  3.7.4  |    2.13.18 |    2.12.20 |
+| 1.10.2 - current   |  3.7.4  |    2.13.18 |    2.12.21 |