The `expect_with_retry` utility expects the lambda to return a
boolean value. However, the previous implementation wrapped the
comparison result `apf_utils.get_matched_packet_counts(...) == 1`
inside a set `{...}`.
This caused the lambda to return a set (e.g., `{True}` or `{False}`),
which is truthy if non-empty, but not the actual boolean result.
This commit removes the unnecessary set wrapper, ensuring the lambda
directly returns the boolean outcome of the packet count comparison
Flag: EXEMPT test only
Bug: 419427388
Test: atest CtsConnectivityMultiDevicesTestCases:ApfV6Test
Change-Id: Idd77d905e5be7933b3213df5cb772773286becfa
7e922cf917