Weld it, only two things will happen:
You prove all the naysayers right and you spend $20 on a new spring and redo your work.
Or
You prove the proponents right and your penny-wise gamble saves you $20
The sky won’t fall, nobody dies, the mower won’t turn into a pile of scrap. It’s not the best fix but if you like to tinker it’s not a big deal.
Heating spring steel without quenching will make it softer, not brittle. I’ve cut/heat/bent coil springs for projects and they worked fine. The hard part will be putting a decent blob of weld on that spot without burning through the spring.
Another frugal option: if both ends are identical, install the spring flipped so the unworn side is on the mount that wears on the spring.