To reproduce this:

$ gradle sdk shims
$ gradle -PTEST_ONLY=true test

The `validateSourceSets` tasks should be run, but aren't.

I discovered this while trying to figure out why JDK-8310654 wasn't caught prior to integration. A GHA test run should have caught the problem, but didn't because validateSourceSets` wasn't run.

We need to add validateSourceSets to the list of tasks that are considered "test" tasks.