Common problem. Nothing to worry about
What techs normally do is drill the rest of the screw out (Sometimes on older models I had to drill out all 3 screws). Be careful not to damage the burner, use a small drill bit about the size of the screw. Replace the broken screw with a similar one.
You're on the right path. That's the only way to replace that igniter.
You probably already know this, but I'll mention it anway: do not use WD40 or anything else flammable to loosen screws on a stove.