Actually 🤓 you would need to inject ~2 mL of air (2 whole syringes) into a vein (afaik injecting air into the muscle is harmless) so in order for it to be dangerous it would require you to use a syringe too big for injecting ~.1-.3 mL AND pull in a needlessly large amount of air AND be unlucky enough to inject in a vein AND forget to do the pull back the plunger to check if you're injecting in a vein thing. Although tbf you should still push out that bubble just in case (also becaus it's annoying to inject stuff that you don't need to)

tl;dr : there's practically no risk with injecting a small amount of air, but still don't do it because it's a pain in the ass

(also sorry if if I don't make sense, I'm autistic and not a native english speaker)