package/python-pypng: add missing python3-zlib dependency
png.py import zlib [1] so python3-zlib needs to be installed at
runtime.
[1] https://gitlab.com/drj11/pypng/-/blob/pypng-0.20220715.0/code/png.py?ref_type=tags#L185
Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/6477656971 (TestPythonPy3Qrcode)
Cc: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 15381b57559182693f6d5530544937f8fcf3b471)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Romain Naour