bpo-34239: Convert test_bz2 to use tempfile

[tjguk]

[Creating tentatively to see how the non-Windows tests run]

test_bz2 currently uses the test.support.TESTFN functionality which creates a temporary file local to the test directory named around the pid.

This can give rise to race conditions where tests are competing with each other to delete and recreate the file.

This change converts the tests to use tempfile.mkstemp which gives a different file every time from the system's temp area

https://bugs.python.org/issue34239

[pfmoore]

LGTM. As an approach, this seems fine, although it's possible that a test that expects the file to not exist in advance could fail if changed to use this approach. That would be fairly easy to spot and fix on a case by case basis, though.

[tjguk]

Thanks @pfmoore. I'll merge this one in. In fact, test_mmap over at #8486 does exactly that so I've had to operate a little differently. As you say: case by case.

[bedevere-bot]

@tjguk: Please replace # with GH- in the commit message next time. Thanks!