tests/test-gendoc-zh_TW.t

rust: update the rust-cpython crate to 0.7.0

This notably brings support for Python 3.10, and includes the panic message
when propagating a Rust panic as a Python exception.

https://github.com/dgrunwald/rust-cpython/blob/master/CHANGELOG.md#070---2021-10-09

Differential Revision: https://phab.mercurial-scm.org/D11630

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_TW
  checking for parse errors