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

-- .mod --
module example.com/split-incompatible/subpkg
-- .info --
{"Version": "v0.1.0"}
-- go.mod --
module example.com/split-incompatible/subpkg

go 1.16
-- subpkg.go --
package subpkg