Setting version to 2.0.21

@rtyley using gha-scala-library-release-workflow · @rtyley using gha-scala-library-release-workflow · commit 5498c84d583a · 2024-01-19T17:14:30.000Z
diff --git a/version.sbt b/version.sbt
@@ -1 +1 @@
-ThisBuild / version := "2.0.21-SNAPSHOT"
+ThisBuild / version := "2.0.21"
