dev/release.sh: improve instruction for pushing the tag

dev/release.sh: improve instruction for pushing the tag

'git push --follow-tags' does a little too much, any spurious tag
object that the releaser have in their local repository will come
along, even though they have nothing to do with the commits being
pushed.

Therefore, we modify the instructions to show a separate and explicit
push of the release tag.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13159)