Source compatibility 21, while readme says 17

Summary

When trying to build the project through the CLI with java 17, I get an error stating source compatibility is 21. When switching to jdk21 this error is resolved.

Steps to reproduce

1. Setup jdk17
2. run ./gradlew build --info

Possible Fix

Either update the README to indicate java 21 is required, or update the source compatibility down to java 17

Logs

...
> Task :compileJava FAILED
Custom actions are attached to task ':compileJava'.
Caching disabled for task ':compileJava' because:
  Build cache is disabled
Task ':compileJava' is not up-to-date because:
  Task has failed previously.
The input changes require a full rebuild for incremental task ':compileJava'.
Compilation mode: in-process compilation
Full recompilation is required because no incremental change information is available. This is usually caused by clean builds or changing compiler arguments.
Compiling with toolchain '/nix/store/xy53lk4001h814d7dwh8f52wcqxrn7rp-openjdk-17.0.11+9/lib/openjdk'.
Compiling with JDK Java compiler API.

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> error: invalid source release: 21