fix: AW-2 json() returns None on a non-UTF-8 body instead of raising

responses.json() catches UnicodeDecodeError alongside JSONDecodeError — text() can raise
it on a non-UTF-8 payload, which is a 'not valid JSON' outcome per the docstring, not an
error to propagate.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/aioweb/responses.py

@@ -92,7 +92,9 @@ class Response:
         """parsed JSON content, or None if not valid JSON"""
         try:
             return _json.loads(self.text())
-        except _json.JSONDecodeError:
+        except (_json.JSONDecodeError, UnicodeDecodeError):
+            # text() decodes the body and can raise UnicodeDecodeError on a non-UTF-8
+            # payload — that's a "not valid JSON" outcome, not an error to propagate
             return None
 
     def raise_for_status(self):