[The Hive] - Replace deprecated utcfromtimestamp usage

[flavienSindou]

          I took the opportunity to correct a well-known deprecated function that has already been replaced in a number of places (i.e. in other connectors). 

If it's annoying, we can remove it. Otherwise, let's fix this.

TLDR: I would leave it, but if it's not a good practice and you don't want to, we can remove it.

Originally posted by @Lhorus6 in https://github.com/OpenCTI-Platform/connectors/pull/3022#discussion_r1862009908