support/testing/tests/package/sample_gst1_python.py: fix flake8 errors

The older version of flake8 on the autobuilders does not support typehints.
As such, flake8 throws the following error when scanning sample_gst1_python:
E999 SyntaxError: invalid syntax

Remove the typehinting from on_message to fix this issue.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/testing/tests/package/sample_gst1_python.py

@@ -8,7 +8,7 @@ gi.require_version('Gst', '1.0')
 from gi.repository import Gst, GLib  # noqa: E402
 
 
-def on_message(bus: Gst.Bus, message: Gst.Message, loop: GLib.MainLoop):
+def on_message(bus, message, loop):
     print('Received Gst.Message.type: {}'.format(message.type))
     if message.type == Gst.MessageType.EOS:
         loop.quit()