* guix/import/go.scm (go-package, go.mod-go-version): New procedures.
(go-module->guix-package): Add the #:go keyword in the generated package
definition if the required go is newer than the default go.
* tests/go.scm (mock-http-get): Use gexps for package arguments.
Change-Id: I8d005740a442330ac307a40a53764c803ceffc4f