test: Pass at most one node group to sync_all

test/functional/rpc_getchaintips.py

@@ -28,7 +28,8 @@ class GetChainTipsTest (BitcoinTestFramework):
         self.split_network()
         self.nodes[0].generatetoaddress(10, self.nodes[0].get_deterministic_priv_key().address)
         self.nodes[2].generatetoaddress(20, self.nodes[2].get_deterministic_priv_key().address)
-        self.sync_all([self.nodes[:2], self.nodes[2:]])
+        self.sync_all(self.nodes[:2])
+        self.sync_all(self.nodes[2:])
 
         tips = self.nodes[1].getchaintips ()
         assert_equal (len (tips), 1)