Regression test for #67360.

This file causes go list to report a "use of internal package
cmd/internal/browser" error. (It is important that this be a real
internal std package.) The line directive caused the position of the
error to lack a column. A bug in the error parser filled in 0, not 1,
for the missing information, and this is an invalid value in the
1-based UTF-8 domain, leading to a panic.

-- foo.go --
//line foo.go:1
package main                    //@ diag(re"package", re"internal package.*not allowed")
import _ "cmd/internal/browser" //@ diag(re`"`, re"could not import")
