Add CI for Java 23

[snicoll]

With Java 23 in its RC phase this week and GA in September, we should add CI for it. Framework supports Java 23 in 6.1+, limiting our Java 23 support to Boot 3.2+.

[snicoll]

So if we want to test, we need to downgrade to Awaitility 4.2.0 again. There is a PR but the project owners haven't reviewed it in months unfortunately.

I've downgraded locally and we're getting more Java Security Manager problem:

• Apache Artemis
• Infinispan 14 is affected (which 3.2.x uses). 15 is not thanks to ISPN-14375.

Courtesy of @mhalbritter, this seems to be due to https://bugs.openjdk.org/browse/JDK-8327134.

We could either disable those tests or use the -Djava.security.manager=allow workaround.

This 3.2.x branch has a number of exclude and is green with Java 23: https://github.com/snicoll/spring-boot/tree/gh-41698

[snicoll]

3.3.x is breaking pretty much any use of Mockito on Java 23 due to couchbase-client shipping an old version of Bytebuddy. We'd need to make an exception to our upgrade policy and upgrade to 3.7.1. I've reported the issue so that we could maybe get a backport of the fix in the version 3.3.x uses.

[snicoll]

Awaitility 4.2.2 has been released with a fix 🥳