community/gnuradio: fix test

Fix failed test qa_correlate_access_code_XX_ts with numpy 2. The error led to rebuild failure on a 3.21 builder.

ERROR: test_payload_lengths (__main__.test_correlate_access_code_XX_ts.test_payload_lengths)
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Traceback (most recent call last):
  File "/home/buildozer/aports/community/gnuradio/src/gnuradio-3.10.11.0/gr-digital/python/digital/qa_correlate_access_code_XX_ts.py", line 104, in test_payload_lengths
    self._variable_payload_t(length)
  File "/home/buildozer/aports/community/gnuradio/src/gnuradio-3.10.11.0/gr-digital/python/digital/qa_correlate_access_code_XX_ts.py", line 77, in _variable_payload_t
    self.assertEqual(header[0] * 256 + header[1], header[2] * 256 + header[3])
                     ~~~~~~~~~~^~~~~
OverflowError: Python integer 256 out of bounds for uint8