package/python-twisted: add missing python3-zlib dependency

Currently the test TestPythonTwisted is not broken [1] since it doesn't
test all modules provided by python-twisted package.

But TestPythonTwisted should have failed due to missing zlib in
twisted/web/client.py and twisted/conch modules.

Due to this, other runtime test like TestPythonPy3MagicWormhole or
TestPythonPy3Txtorcon are currently broken [2][3].

Add missing python3-zlib dependency and update
sample_python_twisted.py to load twisted/web/client that uses zlib
module.

[1] https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992685
[2] https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992687
[3] https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992646

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992687 (TestPythonPy3Txtorcon)

Fixes (partially due to missing python xml dependency):
https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992646 (TestPythonPy3MagicWormhole)

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/python-twisted/Config.in

@@ -7,6 +7,7 @@ config BR2_PACKAGE_PYTHON_TWISTED
 	select BR2_PACKAGE_PYTHON_HYPERLINK # runtime
 	select BR2_PACKAGE_PYTHON_ZOPE_INTERFACE # runtime
 	select BR2_PACKAGE_PYTHON_TYPING_EXTENSIONS # runtime
+	select BR2_PACKAGE_PYTHON3_ZLIB # runtime
 	help
 	  Twisted is an event-driven networking engine written in
 	  Python.

support/testing/tests/package/sample_python_twisted.py

@@ -1,4 +1,5 @@
 from twisted.internet import protocol, reactor, endpoints
+from twisted.web.client import readBody  # noqa: F401
 
 
 class F(protocol.Factory):