Upgrade to Gradle 9.4.1

[8Keep]

#2695

@stephengold mentioned in #2641 that the sdk would block gradle 9, but I see that it is already on netbeans 28 and gradle 9 now.

So it's not a problem for this now, but do we still block jmonkey core on the sdk? Wondering if there is an agreed on policy.

[gemini-code-assist]

Code Review

This pull request updates the Gradle wrapper to version 9.4.1 and adds the JUnit Platform Launcher dependency to the jme3-screenshot-tests module. The reviewer suggested changing the dependency scope from testRuntimeOnly to runtimeOnly to ensure the launcher is transitively available to other modules that depend on this project as a test framework.

[gemini-code-assist]

In Gradle 9, the junit-platform-launcher is required at runtime for executing JUnit 5 tests. Since jme3-screenshot-tests acts as a test framework for other modules (providing base classes in src/main), changing this to runtimeOnly ensures the launcher is transitively available to all consumers of this module. This avoids the need to manually add the launcher to every module's dependencies and ensures consistent test execution across the project.

    runtimeOnly 'org.junit.platform:junit-platform-launcher'

[8Keep]

Oh, it looks like we need to be running jdk 17+ for gradle 9. We need to first update some other dependencies... Trying to untangle the order of operations of all this.

@riccardobl we will need your PR to upgrade android build tools.