What should top-level LICENSE file contain if most files are Apache-2.0, but a few are GPL-2.0-only ?

There are some APIs that examine only the top-level LICENSE file of a project, I believe.  What do those tools expect in such a scenario?

No definitive answer here, but one place where this question is discussed a bit: https://softwareengineering.stackexchange.com/questions/304874/declaring-multiple-licences-in-a-github-project