`set` and `expire` api diffrent handle to 'expire time' param

[lvsoso]

expire: https://github.com/redis/redis-py/blob/42b937fa1f73f3e8251eba5ec8ead2fcbaec7c50/redis/commands/core.py#L1592 set: https://github.com/redis/redis-py/blob/42b937fa1f73f3e8251eba5ec8ead2fcbaec7c50/redis/commands/core.py#L2175

The set api ex should be a interger, but expire's time can use a string(integer in string type) as input.

It make me confusing. Both can also accept string type is more convenient.