tests/avocado/multiprocess: Add asset hashes to silence warnings

tests/avocado/multiprocess: Add asset hashes to silence warnings

The multiprocess test is currently succeeding with an annoying warning:

 (1/2) tests/avocado/multiprocess.py:Multiprocess.test_multiprocess_x86_64:
       WARN: Test passed but there were warnings during execution. Check
       the log for details

In the log, you can find an entry like:

 WARNI| No hash provided. Cannot check the asset file integrity.

Add the proper asset hashes to avoid those warnings.

Message-ID: <20231115145852.494052-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>