Explicitly specify encoding when opening text files in Python code

test/functional/rpc_getblockstats.py

@@ -81,11 +81,11 @@ class GetblockstatsTest(BitcoinTestFramework):
             'mocktime': int(mocktime),
             'stats': self.expected_stats,
         }
-        with open(filename, 'w') as f:
+        with open(filename, 'w', encoding="utf8") as f:
             json.dump(to_dump, f, sort_keys=True, indent=2)
 
     def load_test_data(self, filename):
-        with open(filename, 'r') as f:
+        with open(filename, 'r', encoding="utf8") as f:
             d = json.load(f)
             blocks = d['blocks']
             mocktime = d['mocktime']