Chore: Bump Gradle to version 8.8

[rbair23]

Version 8.6 of Gradle prints a warning with the latest 21.0.3 build of Java. We should upgrade to Gradle 8.8.

[rbair23]

Ah, I'm not sure this actually removes the warning.

[jsync-swirlds]

The warning about 21.0.1 is because the build specifies that java version. Not sure if it's possible, but specifying only the major version (21) would avoid warnings for every bugfix update.

[jjohannes]

The issue should be: Update JDK to 21.0.3

We pin down the exact JDK version for reproducible builds. Gradle does not yet support providing an exact version automatically (gradle/gradle#16628). Therefore, everyone running the build (CI or user) need to make sure the version is installed and Gradle starts with it (documentation will also explain that once #12813 is merged).

Right now the version is defined in multiple places in GH Actions and in one place in Gradle. This could be simplified by defining the version in a separate file and using it in GH Actions via the java-version-file configuration of the action/setup-java. Then there would only be one place. But that's a GH Actions topic. We could create a separate issue for that (cc @rbarkerSL)

Anyway, I created two PRs for both updates (Java and Gradle). This shows the places that need to touched in this repo. I don't know if the JDK version is also defined somewhere else as well in other CI/CD automation outside this repo:

• chore: update to JDK 21.0.3 – for CI and local builds #13756
• chore: update Gradle to 8.8 / setup-gradle to v3.4.2 #13757

[jjohannes]

Gradle has been upgraded to 8.8 by #13757