Aseptic packaging which is what the Swanson’s and anyother brands products in those coated carboard-like packing 9a.K.a Tetrapaks) broth are safe. The aseptic processing has killed thhe harmful bacteria. So long as it was kept refrigerated below 40 deg F after opening it is still safe.
Your frozen veggies if notdefrosted then refrozen are safe.
Combining the two and heating in the microwave in a clean vessel is safe so long as you’ve not introduced bacteria from another source, your food is as safe as it is going to be.