feat: add support for Scala 2.12.16

Closes #469

Author: ckipp01

build.sbt

@@ -2,13 +2,14 @@ import sbtcrossproject.CrossProject
 import sbtcrossproject.CrossType
 
 lazy val munitVersion = "0.7.29"
-lazy val scalametaVersion = "4.4.32"
-lazy val defaultScala212 = "2.12.15"
+lazy val scalametaVersion = "4.5.9"
+lazy val defaultScala212 = "2.12.16"
 lazy val defaultScala213 = "2.13.8"
 lazy val defaultScala3 = "3.1.0"
 lazy val bin212 =
   Seq(
     defaultScala212,
+    "2.12.15",
     "2.12.14",
     "2.12.13",
     "2.12.12",