[3.12] gh-53203: Improve tests for strptime() (GH-125090) (GH-125093)

Run them with different locales and different date and time.

Add the @run_with_locales() decorator to run the test with multiple
locales.

Improve the run_with_locale() context manager/decorator -- it now
catches only expected exceptions and reports the test as skipped if no
appropriate locale is available.
(cherry picked from commit 19984fe024bfd90649f1c36b78c9abf3ed72b27d)