bin/bugzilla_mesa.sh: rework the looping method

bin/bugzilla_mesa.sh: rework the looping method

We don't use DRYRUN (and no others scripts have one) so just drop it.

This allows us to rework the loop to the more commonly used "git .... |
while read foo; do ... done"

That in itself gets rid of the only remaining bashism and we can toggle
the shebang to /bin/sh.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>