Explicitly specify encoding when opening text files in Python code

test/functional/wallet_multiwallet.py

@@ -88,7 +88,7 @@ class MultiWalletTest(BitcoinTestFramework):
         self.nodes[0].assert_start_raises_init_error(['-walletdir=bad'], 'Error: Specified -walletdir "bad" does not exist')
         # should not initialize if the specified walletdir is not a directory
         not_a_dir = wallet_dir('notadir')
-        open(not_a_dir, 'a').close()
+        open(not_a_dir, 'a', encoding="utf8").close()
         self.nodes[0].assert_start_raises_init_error(['-walletdir=' + not_a_dir], 'Error: Specified -walletdir "' + not_a_dir + '" is not a directory')
 
         self.log.info("Do not allow -zapwallettxes with multiwallet")