version.sh: Print versions based on the last git tag for release branches

release branches are detected by checking if "git" is not in RELEASE
This changes "N-64706-g2f71aeb" to "n2.3-8-g2f71aeb"
for git master theres no change

This should improve the readability of lists of versions which come from
more than 1 release branch or master + release. fate.ffmpeg.org is
one possible example

Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit ee606fd0)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>