cmd/go/internal/modload: don't report path errors when loading retractions
    
    When we load module retractions from the latest version of a module,
    it's possible that the latest version has a different module path than
    the version we're loading. This can happen when a module is renamed or
    a go.mod file is added for the first time.
    
    We should not report an error in this case. Retractions should still
    apply to old aliases of a module.
    
    Fixes #41350
    
    Change-Id: If1bc0b6b2b26fc7023e02fc211aa0cd8eb00796e
    Reviewed-on: https://go-review.googlesource.com/c/go/+/255961
    Trust: Jay Conrod <jayconrod@google.com>
    Run-TryBot: Jay Conrod <jayconrod@google.com>
    Reviewed-by: Bryan C. Mills <bcmills@google.com>
    TryBot-Result: Go Bot <gobot@golang.org>