The v1.0.0 release of example.com/retract/incompatible retracts
v2.0.0+incompatible.

-- .mod --
module example.com/retract/incompatible

go 1.16

retract v2.0.0+incompatible
-- .info --
{"Version":"v1.0.0"}
-- go.mod --
module example.com/retract/incompatible

go 1.16

retract v2.0.0+incompatible
-- incompatible.go --
package incompatible
