test-url: move from dict() construction to {} literals

The latter are both faster and more consistent across Python 2 and 3.

tests/test-url.py

@@ -5,7 +5,7 b' def check(a, b):'
         print (a, b)
 
 def cert(cn):
-    return dict(subject=((('commonName', cn),),))
+    return {'subject': ((('commonName', cn),),)}
 
 from mercurial.sslutil import _verifycert