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": "v0.1.0"}
-- go.mod --
module example.net/ambiguous

go 1.16
-- nested/pkg/pkg.go --
// Package pkg exists in both example.net/ambiguous v0.1.0
// and example.net/ambiguous/nested v0.1.0
package pkg