Written by hand.

Test module containing a package that is also provided by a nested module tagged
with the same version.

-- .mod --
module example.net/ambiguous

go 1.16
-- .info --
{"Version": "v0.2.0"}
-- go.mod --
module example.net/ambiguous

go 1.16
-- nested/pkg/README.txt --
// Package pkg no longer exists in this module at v0.2.0.
// Find it in module example.net/ambiguous/nested instead.