build(gradle): Fix running OrtConfigurationTest on Windows

This prevents errors like

    Unable to make field private static final java.util.Map
    java.lang.ProcessEnvironment.theCaseInsensitiveEnvironment accessible:
    module java.base does not "opens java.lang" to unnamed module @673fdbc

when running `OrtConfigurationTest` on Windows with Temurin JDK 21.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

buildSrc/src/main/kotlin/ort-kotlin-conventions.gradle.kts

@@ -228,6 +228,7 @@ tasks.withType<Test>().configureEach {
         // See https://kotest.io/docs/next/extensions/system_extensions.html#system-environment.
         jvmArgs(
             "--add-opens", "java.base/java.io=ALL-UNNAMED",
+            "--add-opens", "java.base/java.lang=ALL-UNNAMED",
             "--add-opens", "java.base/java.util=ALL-UNNAMED",
             "--add-opens", "java.base/sun.nio.ch=ALL-UNNAMED"
         )