on_stderr function doesn't excute

I have a simple on_stderr function in my setup function.
```
on_stderr = function(t, job, data, name)
print("aaaaaaaaaaaaaaaaaaaaaa")
require("toggleterm").toggle_all()
end,
```
This prints and toggles the terminal if my terminal outputs to stderr. However, it doesn't seem to be working. I've tried using on_stdout and it works perfectly fine.

nvim version: v0.8.1