unplanned fungi growing in flowerpot question?

The mushrooms themselves certainly could have been poisonous if you ate them, but they can't translocate their alkaloids into your herbs, and composting them, or allowing the remains to become part of the soil in the pot is not a danger. Just disturb them when you see them - they're remarkably fragile.

Not to worry. They haven't tainted your herbs. They grew because they are a fungi and some fungi spores landed there. My guess is that it was damp for an extended period - have you had some rainy weather?

I would never eat a mushroom that I didn't know for certain was safe. If they grow again, just pull them out and throw them away.

And enjoy your herbs!