Adjust test for 3.10 semantics of is_private on networks

In 3.10 and below, is_private checks whether the network and broadcast
address are both private.
In later versions (where the test wss backported from), it checks
whether they both are in the same private network.

For 0.0.0.0/0, both 0.0.0.0 and 255.225.255.255 are private,
but one is in 0.0.0.0/8 ("This network") and the other in
255.255.255.255/32 ("Limited broadcast").

Lib/test/test_ipaddress.py

@@ -2283,7 +2283,7 @@ def testReservedIpv4(self):
         self.assertEqual(True, ipaddress.ip_network('0.0.0.0').is_unspecified)
 
     def testPrivateNetworks(self):
-        self.assertEqual(False, ipaddress.ip_network("0.0.0.0/0").is_private)
+        self.assertEqual(True, ipaddress.ip_network("0.0.0.0/0").is_private)
         self.assertEqual(False, ipaddress.ip_network("1.0.0.0/8").is_private)
 
         self.assertEqual(True, ipaddress.ip_network("0.0.0.0/8").is_private)