This is an example of where the exact wording of the various codes matters.

Your gas utility will have it's codes posted on the internet. A typical requirement will be that anything that sparks (like a breaker) has to be at least 3 ft (straight line, any angle) from anything that vents gas (lie a regulator).

I would assume that a GFCI sparks when it opens a circuit under load. I would assume that a simple gas line does N OT vent gas; therefore, there is no spacing required.