cmd/go: bad error message when import path does not contain a package

[aarzilli]

$ go version
go version devel go1.20-1eb0465fa5 Tue Dec 6 05:12:12 2022 +0000 linux/amd64

With go.mod:

module whatever

go 1.19

require github.com/aclements/go-z3 v0.0.0-20220809013456-4675d5f90ca5 // indirect

and main.go:

package main

import (
	_ "github.com/aclements/go-z3"
)

func main() {
}

running go build or go run says:

main.go:4:2: no required module provides package github.com/aclements/go-z3; to add it:
	go get github.com/aclements/go-z3

which is wrong and the suggested action is a noop. In reality the problem is that github.com/aclements/go-z3 is not a package.

[dmitshur]

CC @bcmills, @matloob.

[bcmills]

Duplicate of #46806