build fails with JDK 21

[defaultbranch]

Expected Behavior

When cloning the repository and running ./gradlew --console plain installDist (as in the project README.md), the project should build.

Actual Behavior

After gradlew downloaded gradle-7.4.2-all.zip, the build failed:

FAILURE: Build failed with an exception.

* Where:
Settings file '/home/cfuchs/projects/rsocket-cli/settings.gradle'

* What went wrong:
Could not compile settings file '/home/cfuchs/projects/rsocket-cli/settings.gradle'.
> startup failed:
  General error during conversion: Unsupported class file major version 65
  
  java.lang.IllegalArgumentException: Unsupported class file major version 65

Steps to Reproduce

In an environment where javac -version reports version 21, run:

git clone https://github.com/rsocket/rsocket-cli.git
cd rsocket-cli/
./gradlew --console plain installDist

Possible Solution

Workaround: switch to JDK 17 (Debian: sudo update-alternatives --config java).

Your Environment

• latest rsocket, at the time of this bug the HEAD commit was 9cd4656 Update all dependencies + JDK 17 (#124)
• Debian 12 with packages temurin-21-jdk and openjdk-17-jdk, no preinstalled gradle (only using gradlew wrapper).