Update scala-library to 2.12.21

Author: scala-steward

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        scala: [2.12.20, 2.13.15, 3.3.6]
+        scala: [2.12.21, 2.13.15, 3.3.6]
         java: [zulu@8]
     runs-on: ${{ matrix.os }}
     steps:

build.sbt

@@ -7,7 +7,7 @@ import microsites.*
 ThisBuild / mimaFailOnNoPrevious := false
 val mimaPreviousVersion = "2.2.0"
 
-lazy val Scala212 = "2.12.20"
+lazy val Scala212 = "2.12.21"
 lazy val Scala213 = "2.13.15"
 lazy val Scala3 = "3.3.6"