[Task]: Update mypy type checker in tox.ini

### What needs to happen?

If we try to update mypy-protobuf in build-requirements.txt to a latest version and run myypy==0.782(this is what we use currently to run mypy) type checker on the stubs generated by mypy-protobuf, we will see some errors which are wrong.


Update mypy to the latest version since the current version we use (0.782) was released almost 2 years back.

### Issue Priority

Priority: 3 (nice-to-have improvement)

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