Refactor code quality issues (#2001)

src/pretix/helpers/jsonlogic.py

@@ -94,7 +94,7 @@ def merge(*args):
     """Implements the 'merge' operator for merging lists."""
     ret = []
     for arg in args:
-        if isinstance(arg, list) or isinstance(arg, tuple):
+        if isinstance(arg, (list, tuple)):
             ret += list(arg)
         else:
             ret.append(arg)