Run test suites like how CPython runs theirs by fanninpm · Pull Request #3807 · RustPython/RustPython

The extra flags come from the `buildbottest` rule in CPython's Makefile.
This will enable checking the tests we've been skipping by default (such
as network-based tests). This will also report the top 10 slowest tests
and will mark a test as failed if it altered the execution environment.

"ValueError: illegal environment variable name" likely comes from the
`--fail-env-changed` switch we're now using.