Update Gradle to 8.10.2 (#684)

Verify wrapper JAR according to:
https://docs.gradle.org/current/userguide/gradle_wrapper.html#wrapper_checksum_verification

pkl-gradle/pkl-gradle.gradle.kts

@@ -94,3 +94,9 @@ signing {
     }
   }
 }
+
+// As of Gradle 8.10, the following is necessary to avoid a test compile error.
+// (Apparently, gradle-api.jar now contains metadata that causes kotlinc to enforce Gradle's Kotlin
+// version.)
+// A more robust solution would be to port plugin tests to Java.
+tasks.compileTestKotlin { kotlinOptions { freeCompilerArgs += "-Xskip-metadata-version-check" } }