Package outside of dependency constraints - But I don't use the package

When I try to run unit tests for my program, I get the following warning:

warning NU1608: Detected package version outside of dependencyconstraint: Microsoft.Build.Utilities.Core 15.3.409 requires Microsoft.Build.Framework (= 15.3.409) but version Microsoft.Build.Framework 17.0.0 was resolved.

That sounds pretty self-explanatory. But none of the mentionened packages are references in my test project. They aren't referenced the the other projects in the solution as well.

Can it be that it is an implicit reference, from another package I use? And if so, how do I fix the dependency constraint issues?