bpo-29571 - test_re needs en_US.iso88591 locale check in test_locale_flag()

[Naman-Bhalla]

The fix proposes to add a check for en_US.iso88591 in test_localeflag. This should fix test_re for languages like en_IN till another fix is done, which is requiring a lot of code.
The error for en_IN locale and some others can also be found here :- https://hastebin.com/ecabuvovuj.sql

[the-knights-who-say-ni]

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[serhiy-storchaka]

This doesn't fix the issue.

1. Locale-depending regular expressions work only with 8-bit encodings. UTF-8 is not supported.
2. en_US.iso88591 is not particularly interesting for testing. And it may be not supported on Windows.
3. This patch changes program global locale. This affects all following tests.