Written by hand.
Test case for getting a package that has been moved to a nested module,
with a +incompatible verison (and thus no go.mod file) at the root module.

-- .mod --
module example.com/split-incompatible
-- .info --
{"Version": "v2.1.0-pre+incompatible"}
-- README.txt --
subpkg has moved to module example.com/split-incompatible/subpkg