Fix a mistake in isSet() deprecated message doc

[marcmonfort]

Fix a mistake in isSet() deprecated message where it recommends to use notify_all() instead of is_set().

[bedevere-bot]

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Please add it using the blurb_it web app or the blurb command-line tool.

[ghost]

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[miss-islington]

Thanks @marcmonfort for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10, 3.11.
🐍🍒⛏🤖

[miss-islington]

Sorry @marcmonfort and @JelleZijlstra, I had trouble checking out the 3.11 backport branch.
Please backport using cherry_picker on command line.
cherry_picker 7f685683f8e23084aa8b05f0c186f5c962f1db29 3.11

[miss-islington]

Sorry, @marcmonfort and @JelleZijlstra, I could not cleanly backport this to 3.10 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 7f685683f8e23084aa8b05f0c186f5c962f1db29 3.10

[miss-islington]

Thanks @marcmonfort for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[miss-islington]

Sorry, @marcmonfort and @JelleZijlstra, I could not cleanly backport this to 3.11 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 7f685683f8e23084aa8b05f0c186f5c962f1db29 3.11

[JelleZijlstra]

This was already fixed in e534440 / #96297, I just merged an empty commit. That's why the backports failed.