Update scala-compiler, scala-library to 2.12.21

Author: scala-steward

.github/workflows/scala.yml

@@ -18,13 +18,13 @@ jobs:
         include:
           - scala: 2.11.12
             sbt-args: --addPluginSbtFile=project/plugins.sbt.scala-js.1.x
-          - scala: 2.12.11
+          - scala: 2.12.21
             sbt-args: --addPluginSbtFile=project/plugins.sbt.scala-js.1.x
           - scala: 2.13.4
             sbt-args: --addPluginSbtFile=project/plugins.sbt.scala-js.1.x
           - scala: 2.10.7
           - scala: 2.11.12
-          - scala: 2.12.11
+          - scala: 2.12.21
           - scala: 2.13.4
 
     steps: