SpringBoot "languageVersion is final and cannot be changed" when using Gradle 8.3 and configuring the Java toolchain's language version

When using GraalVM gradle plugin (v0.9.26) with Spring Boot gradle plugin (v3.1.3), languageVersion cannot be set:

java {
    toolchain {
        languageVersion.set(JavaLanguageVersion.of(20)) // <-- the error occurs here
    }
}

graalvmNative {
    binaries {
        named("main") {
            javaLauncher.set(javaToolchains.launcherFor {
                languageVersion.set(JavaLanguageVersion.of(20))
            })
        }
    }
}

The following error occurs:

* What went wrong:
The value for property 'languageVersion' is final and cannot be changed any further.

Here is a reproducer by @jamesward: https://github.com/graalvm/native-build-tools/issues/486#issuecomment-1714191396

Also, @melix explained how to fix it: https://github.com/graalvm/native-build-tools/issues/486#issuecomment-1714236655

Comment From: wilkinsona

Closing in favor of #37343.