Some parametrizations of test_write_non_timestamp_index hang for some python 3.8 builds

[jjerphan]

Have been observed in recent PRs including #233, #240, #242, #245

Instance of logs:

• linux linux_64_aws_sdk_cpp1.11.210azure_core_cpp1.11.1libevent2.1.10numpy1.22python3.8.____cpython from 75bd141 @ [rc] Add extra alternative builds on aws-sdk-cpp==1.11.210 #245
• linux linux_64_aws_sdk_cpp_azure_core_cpp_libevent_numpy1.22python3.8.____cpython from 75bd141 @ [rc] Add extra alternative builds on aws-sdk-cpp==1.11.210 #245

Blocked without errors around 90%:

...
test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-True-range] 
[gw0] [ 90%] PASSED python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-True-range] 
python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-True-int64] 
[gw0] [ 90%] PASSED python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-True-int64] 
python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-False-range] 
[gw0] [ 90%] PASSED python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-False-range] 
python/tests/unit/arcticdb/version_store/test_write.py::test_write_non_timestamp_index[lmdb_version_store_v2-False-False-int64] 

[jjerphan]

Likely related to pytest-xdist, not the tests themselves.

See #245.