DOC: Fix undefined request_opts in MNIST download example

[EishaEnan]

Summary

Fixes an undefined variable (request_opts) in the MNIST download example.

Problem

The documentation example includes the following line:

resp = requests.get(base_url + fname, stream=True, **request_opts)

However, request_opts is never defined in the example, which results in a NameError when users try to run the code.

Solution

Removed the unused **request_opts argument from the requests.get call to ensure the example runs correctly without requiring additional context.

Changes

- resp = requests.get(base_url + fname, stream=True, **request_opts)
+ resp = requests.get(base_url + fname, stream=True)

Impact

• Prevents runtime errors for users following the tutorial
• Improves clarity and reproducibility of the documentation example
• Keeps the example minimal and beginner-friendly

Notes

This change keeps the example aligned with standard usage of requests.get and avoids introducing unnecessary variables.

[bsipocz]

OK, let's think about this as it's defined in L89 which we hide from the rendered output. Maybe we should include an empty version before that cell though?

cc @rossbar as the original author of hiding the content of the dict