package/python-django: add missing python-zlib runtime dependency

Tree django core files are using "import zlib" and requires
BR2_PACKAGE_PYTHON3_ZLIB to be enabled.

django/core/cache/backends/filebased.py:import zlib
django/core/files/images.py:import zlib
django/core/signing.py:import zlib

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/4322819300

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/python-django/Config.in

@@ -2,6 +2,7 @@ config BR2_PACKAGE_PYTHON_DJANGO
 	bool "python-django"
 	select BR2_PACKAGE_PYTHON3_UNICODEDATA
 	select BR2_PACKAGE_PYTHON3_PYEXPAT
+	select BR2_PACKAGE_PYTHON3_ZLIB # runtime
 	select BR2_PACKAGE_PYTHON_ASGIREF # runtime
 	select BR2_PACKAGE_PYTHON_SQLPARSE # runtime
 	help