chore: update to Unity 6000.3.12f1 (#2602)

Author: github-actions[bot]

scripts/ci-env.ps1

@@ -14,7 +14,7 @@ switch ($name) {
         return "6000.0.68f1"
     }
     "unity6000.3" {
-        return "6000.3.10f1"
+        return "6000.3.12f1"
     }
     Default {
         throw "Unkown variable '$name'"