fix: bip21.py: add missing import

urllib.parse needs to be explicitly imported for e.g. urllib.parse.urlparse to work.
I think this was not erroring only because urllib.parse is imported in other modules.

electrum/bip21.py

@@ -1,4 +1,5 @@
 import urllib
+import urllib.parse
 import re
 from decimal import Decimal
 from typing import Optional