bpo-33759: Fix test.test_xmlrpc.ServerProxyTestCase. (GH-7362) (GH-7371)

It depended on a global variable set by other tests.
(cherry picked from commit 7cfd8c6a1b)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/test/test_xmlrpc.py

@@ -1175,7 +1175,9 @@ class GzipUtilTestCase(unittest.TestCase):
 class ServerProxyTestCase(unittest.TestCase):
     def setUp(self):
         unittest.TestCase.setUp(self)
-        self.url = URL
+        # Actual value of the URL doesn't matter if it is a string in
+        # the correct format.
+        self.url = 'http://fake.localhost'
 
     def test_close(self):
         p = xmlrpclib.ServerProxy(self.url)