[3.11] gh-104992: [What's New in 3.11] Document unittest.TestProgram.usageExit's deprecation (GH-104994) (#105010)

gh-104992: [What's New in 3.11] Document unittest.TestProgram.usageExit's deprecation (GH-104994)

Document unittest.TestProgram.usageExit's pending removal in 3.13
(cherry picked from commit 7df861c23cd61e7c55943d4036ea5c6b1df5cb49)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>
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