chore: update to Unity 6000.0.39f1 (#2030)

Author: github-actions[bot]

scripts/ci-env.ps1

@@ -20,7 +20,7 @@ switch ($name) {
         return "2023.2.20f1"
     }
     "unity6000" {
-        return "6000.0.38f1"
+        return "6000.0.39f1"
     }
     Default {
         throw "Unkown variable '$name'"