“Jif” is the original pronunciation. It is a pun, a play on the word “jif” short for “jiffy” meaning a short amount of time, as in “I’ll send it to you in a gif”. The newer pronunciation has become popular based on the fallacious reasoning that an acronym should be pronounced the same as its constituent words, which isn’t a thing at all.
Language evolves, and both pronunciations are common enough to be considered acceptable. The only way to be wrong about how to pronounce the word is to claim one of the pronunciations is wrong.