If we want to validate a tag when using shallow clones, we need to ensure
the tag is imported to the clone. Adding to extra_refs allows this to happen
ensuring tag validation in shallow clones works.
(Bitbake rev: 03945475886b8d31c7eccc80fe594ab5306bcf5d)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>