Update scala to 2.12.15

Author: sh0hei

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        scala: [2.11.12, 2.12.13, 2.13.5]
+        scala: [2.11.12, 2.12.15, 2.13.5]
         java: [adopt@1.8]
     runs-on: ${{ matrix.os }}
     steps:

build.sbt

@@ -7,7 +7,7 @@ import ReleaseTransformations._
 val Scala211 = "2.11.12"
 val NativeCond = s"matrix.scala == '$Scala211'"
 
-ThisBuild / crossScalaVersions := Seq(Scala211, "2.12.13", "2.13.5")
+ThisBuild / crossScalaVersions := Seq(Scala211, "2.12.15", "2.13.5")
 ThisBuild / scalaVersion := Scala211
 
 ThisBuild / githubWorkflowPublishTargetBranches := Seq()