[fix] fix KeyError: 'ipv6'

tests/units/network/test_network.py requires a call to searx.network.network.initialize
Depending of the test order execution, this function was sometimes call in another test,
sometimes not.

This commit ensure there is a call to initialize()

tests/unit/network/test_network.py

@@ -4,12 +4,15 @@ from mock import patch
 
 import httpx
 
-from searx.network.network import Network, NETWORKS
+from searx.network.network import Network, NETWORKS, initialize
 from searx.testing import SearxTestCase
 
 
 class TestNetwork(SearxTestCase):
 
+    def setUp(self):
+        initialize()
+
     def test_simple(self):
         network = Network()