Fix updating of scala versions with scala steward

.scala-steward.conf

@@ -1,5 +1,10 @@
-# Latest version of jgit which was compiled with JDK 8 which this project targets
-updates.pin = [{ groupId = "org.eclipse.jgit", version = "5.13.0.202109080827-r" }]
+updates.pin = [
+  # Latest version of jgit which was compiled with JDK 8 which this project targets
+  { groupId = "org.eclipse.jgit", version = "5.13.0.202109080827-r" },
+  # Only do updates for Scala 2.12 series
+  { groupId = "org.scala-lang", artifactId = "scala-library", version = "2.12." }
+]
+
 updates.ignore = [
   { groupId = "org.eclipse.jgit" }
 ]

build.sbt

@@ -72,7 +72,7 @@ inThisBuild(
     licenses := Seq(
       "Apache-2.0" -> url("http://www.apache.org/license/LICENSE-2.0")
     ),
-    scalaVersion := "2.12.17", // scala-steward:off
+    scalaVersion := "2.12.20",
     versionScheme := Some("semver-spec")
   )
 )