ICU-22721 Update filtration_test for Python 3.13

[yselkowitz]

unittest.makeSuite() was deprecated in Python 3.11 and removed in 3.13: https://docs.python.org/3.13/whatsnew/3.13.html#unittest

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22721
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[CLAassistant]

All committers have signed the CLA.

[echeran]

The change looks good, and thanks for making the change. I updated the PR with appropriate details.

The one last thing required is for the commit message to be prefixed with "ICU-22721" followed by a space. Can you do that? If not, one of us can. FWIW, the easiest way to achieve that is to use the PR Checker Bot. In the table of PR checks, in the row that says "jira-ticket", click the "Details" link. The opportunity to squash the one commit won't affect the code, and in this case won't affect the number of commits on the branch, but you can use it to reword the commit message.

[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

~ Your Friendly Jira-GitHub PR Checker Bot

[yselkowitz]

@echeran should be fixed now, all tests passed.