KVS based on `ApifyFileSystemKeyValueStoreClient` can get purged twice

[Pijukatel]

Can be reproduced by this test:

async def test_no_double_purge_for_filesystem_storage_client() -> None:
    expected_value = 'some value'
    expected_key = 'some key'

    async with Actor():
        await Actor.set_value(expected_key, expected_value)
        # RQ uses KVS under the hood for persistence, so it will try to open same default KVS as it was already opened,
        # but based on different client - FileSystemStorageClient.
        await Actor.open_request_queue()
        assert expected_value == await Actor.get_value(expected_key)

Draft fix here:
master...prevent-double-purging-of-kvs

Let's not merge the fix as there are open questions about INPUT file expected behavior, which is the only reason for having ApifyFileSystemKeyValueStoreClient, which is the root cause of this issue

Merge the quickfix only if someone reports severe issues.