Somebody claiming to be Stephen Paul Weber wrote:
>https://go.dev/ref/mod says a module in a subdirectory has a tag prefixed with
>the subdirectory.

Dang.  This patch as written causes import of guix import go
github.com/jackc/pgx/v4 to fail. The /v4 suffix in this case appears to refer to
a branch and not a subdirectory, but the syntax is identical?