Configure JDK 23 early access CI build

[sbrannen]

Overview

Java 23 early access builds are already available.

Our CI currently maintains JDK 21 and JDK 22 compatibility builds. We should do the same for JDK 23 as soon as the test suite is usable with early access versions.

Related Issues

• Configure JDK 22 early access CI build #31459

[sbrannen]

An initial attempt via ./gradlew test -PtestToolchain=23 reveals issues with Mockito (Byte Buddy).

Caused by: java.lang.IllegalArgumentException: Java 23 (67) is not supported by the current version of Byte Buddy which officially supports Java 22 (66) - update Byte Buddy or set net.bytebuddy.experimental as a VM property

[snicoll]

Gradle does not yet support Java 23, see https://docs.gradle.org/current/userguide/compatibility.html#java

[snicoll]

So it turns out that it works for our purpose with Gradle 8.7 already (ping @ljacomet). There are a number of failures that I am investigating.

First thing is that Awaitility does not work with EA builds, see awaitility/awaitility#279

[snicoll]

This is blocked by #33144

Here's a build scan against 6.1.x with 23.ea.29: https://ge.spring.io/s/uyz33y2i7ezac/tests/overview?outcome=FAILED

[snicoll]

Gradle does not yet support Java 23, see https://docs.gradle.org/current/userguide/compatibility.html#java

It turns out it doesn't affect us as much as I thought. We're using the toolchains to run the tests, which doesn't trigger any compilation and that work pretty much out of the box. As @ljacomet explained to me, the problem is incremental compilation and others advanced compiled scripts use cases. We don't use any of that.