pysss_murmur: Fix DeprecationWarning PY_SSIZE_T_CLEAN
src/tests/pysss_murmur-test.py:93: DeprecationWarning: PY_SSIZE_T_CLEAN will be required for '#' formats
hash_val = pysss_murmur.murmurhash3(sid_str, 0, seed)
src/tests/pysss_murmur-test.py:96: DeprecationWarning: PY_SSIZE_T_CLEAN will be required for '#' formats
hash_val = pysss_murmur.murmurhash3(sid_str, len(sid_str), seed)
These were introduced by https://bugs.python.org/issue36381 to warn about
an upcoming Python C API change. The meaning of PY_SSIZE_T_CLEAN is described
in https://python.readthedocs.io/en/stable/c-api/arg.html#strings-and-buffers.
Reviewed-by: Pavel Březina <pbrezina@redhat.com>\
Reviewed-by: Tomáš Halman <thalman@redhat.com>