The jacoco plugin was applied on the wrong Project object which lead to multiple workarounds:
 * somehow `apply plugin:` binds to the script default project which is rootProject
 * so the plugin wasn't applied to currentProject
 * so it didn't register .jacoco on the Test tasks
 * so manual `applyTo()` was required
 * calling `applyTo test` resolved to `rootProject.jacoco.applyTo(currentProject.tasks.test)` (because the currentProject.jacoco wasn't registered!)
 * which lead to a cross-project configuration leak, and we had the warning:

> Task :*:test
Resolution of the configuration :jacocoAgent was attempted from a context different than the project context. Have a look at the documentation to understand why this is a problem and how it can be resolved. This behavior has been deprecated. This will fail with an error in Gradle 9.0. For more information, please refer to https://docs.gradle.org/8.2/userguide/viewing_debugging_dependencies.html#sub:resolving-unsafe-configuration-resolution-errors in the Gradle documentation.

Because of the manual applyTo() call the project object was always rootProject which set the wrong destinationFile and tasks overwrote each others' outputs. The workaround to manually split these files is no longer necessary after the previous commit.

… test data.