Accept extra arguments to outputframe

The `picamera2` package now gives extra arguments to
`PicameraStreamOutput.outputframe`.
I've added two additional optional arguments to fix this, in a
backwards-compatible way.

Author: rwb27

src/labthings_picamera2/thing.py

@@ -92,7 +92,7 @@ def __init__(self, stream: MJPEGStream, portal: BlockingPortal):
         self.stream = stream
         self.portal = portal
 
-    def outputframe(self, frame, _keyframe=True, _timestamp=None):
+    def outputframe(self, frame, _keyframe=True, _timestamp=None, _packet=None, _audio=False):
         """Add a frame to the stream's ringbuffer"""
         self.stream.add_frame(frame, self.portal)