test: Fix Comment Typo in BitcoinTestFramework

Missing "override" in comment describing use of set_test_params

Author: joelklabo

test/functional/test_framework/test_framework.py

@@ -332,7 +332,7 @@ def shutdown(self):
 
     # Methods to override in subclass test scripts.
     def set_test_params(self):
-        """Tests must this method to change default values for number of nodes, topology, etc"""
+        """Tests must override this method to change default values for number of nodes, topology, etc"""
         raise NotImplementedError
 
     def add_options(self, parser):