cython: fix the usage of cython #308

Job	Run time
Build source distribution	12s
Build source distribution	12s
Integration Tests (Cassandra)	5m 10s
Integration Tests (Cassandra)	5m 10s
Build wheels (ubuntu-20.04)	1h 20m 35s
Build wheels (ubuntu-20.04)	1h 20m 35s
docker	14m 53s
docker	14m 53s
Build wheels (windows-2019)	12m 3s
Build wheels (windows-2019)	12m 3s
Build wheels (macos-11)	1s
Build wheels (macos-11)	1s
Integration Tests (Scylla)	4m 12s
Integration Tests (Scylla)	4m 12s
Integration Tests (Scylla Cloud Bundle)	5m 32s
Integration Tests (Scylla Cloud Bundle)	5m 32s
Integration Tests (Scylla Enterprise)	4m 35s
Integration Tests (Scylla Enterprise)	4m 35s
upload_pypi	0s
upload_pypi	0s
	4h 14m 26s

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