To my surprise, the OED says both are valid uses, and "mike" actually might predate "mic". Its earliest example for mike is from 1926, while the earliest for mic is 1961.

You're on Air viii., 1926: "The man at the ‘mike’ watches..and tells the audience the type of play."

Singers' Glossary of Show Business Jargon, 1961: "Microphone: (Abbr. mike or mic)."

“mic” when referring to microphones? It’s super common in the audio world and probably others like film.

Also it’s exactly the sequence of letters the word starts with, unlike the homonym “mike”.

Curious why this is getting to your pedantic side?