Type cast fix for examples/notebooks/Tutorial-Prompt-Optimization.ipynb

[mounir-portia]

Peeps,

Love this repo so thanks a mil! Wanted to flag that for examples/notebooks/Tutorial-Prompt-Optimization.ipynb to work, I had to modify a line in the eval_sample function:
y = tg.Variable(y, requires_grad=False, role_description="correct answer for the query")
should actually be y = tg.Variable(int(y), requires_grad=False, role_description="correct answer for the query").

I believe the process of populating y in the class BigBenchHard ends up populating it as a numpy.int64 so that throws off the Variable declaration afterwards since it's expecting Union[str, bytes] as the data type for the value.

Hope this makes sense, and huge love and respect for your work on TG,
Mounir (mostly an eternal noob so apologies if I missed something obvious)