docs: fix a syntax issue in document breaking changes

[illusory-dream]

Description of Change

Sample code written in the Breaking Changes does not work, which was added by @nornagon in #42053

Checklist

• PR description included and stakeholders cc'd
• relevant documentation, tutorials, templates and examples are changed or added

Release Notes

Notes: none

[welcome]

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[nikwen]

Nice, looks great. 👍

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[release-clerk]

No Release Notes

[trop]

I have automatically backported this PR to "32-x-y", please check out #44903

[trop]

I have automatically backported this PR to "33-x-y", please check out #44904

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I have automatically backported this PR to "34-x-y", please check out #44905