[CHORE] flake8 issues E402, E721 and F821 (#1874)

* F821: undefine name
disabled and logged webhook_listener for opennode and lnpay because they are obviously not working
* E402: module level import not at top of file
* E721 fixes, only popped up for python3.9 not 3.10

tests/core/test_db.py

@@ -9,4 +9,4 @@ from lnbits.db import POSTGRES
 async def test_date_conversion(db):
     if db.type == POSTGRES:
         row = await db.fetchone("SELECT now()::date")
-        assert row and type(row[0]) == date
+        assert row and isinstance(row[0], date)