Fix test dependency
Fix test dependency

When running the `LfMerge.Core.Tests` we expect to find `FixFwData`,
therefore this has to be a dependency even though it's not
explicitly used in the code.

This allows to build the solution and get a successful test run.

sillsdev/LfMerge,sillsdev/LfMerge,sillsdev/LfMerge