scripted-diff: Bump copyright headers

The previous diff touched most files in ./test/, so bump the headers to
avoid having to touch them again for a bump later.

-BEGIN VERIFY SCRIPT-
./contrib/devtools/copyright_header.py update ./test/
-END VERIFY SCRIPT-

test/functional/feature_bind_extra.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright (c) 2014-2021 The Bitcoin Core developers
+# Copyright (c) 2014-2020 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """