Unless the soil was previously a rubbish tip, a chemical factory, or owned by weirdo who liked to water their garden with leaded petrol, the amount of lead in the soil is likely to be minuscule. (And other heavy metals too. It would just whatever the background level is, which is fine for food, all soils our farmed food is grown in have naturally present trace metals to various degrees). But if it’s not in your comfort zone, then that’s ok! Just grow the pumpkins for ornamental value, or learning a new skill, or still life subjects for your art, or providing flowers for pollinators, and eventually compost for the garden to keep the worms happy and soil healthy. The goal doesn’t have to be food production, it’s still enjoyable to watch things grow.