test_broadcast_kv_store does not use await or yield at all, so
there is no need to mark it with "asyncio" mark.
tested using
```
SCYLLA_HOME=$HOME/scylla build/cmake/scylla --overprovisioned --developer-mode=yes --consistent-cluster-management=true --experimental-features=broadcast-tables
...
pytest broadcast_tables/test_broadcast_tables.py
```
the test still passes.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13006
991379bdb3