Build/Test Tools: Update the sinon dependency to version 22.0.0.

[tan7vir]

This updates the sinon development dependency from 16.1.3 to the latest 22.0.0, as requested on the ticket, and regenerates package-lock.json. sinon-test and qunit are left unchanged, and the lockfile changes are confined to the sinon dependency subtree.

The bump surfaces the timezone test failures noted on the ticket. The communityEvents.getTimeZone tests in tests/qunit/wp-admin/js/dashboard.js stubbed Intl.DateTimeFormat.prototype.resolvedOptions, but getTimeZone() reads from a freshly constructed Intl.DateTimeFormat() instance. From sinon 17 onwards, the bundled @sinonjs/fake-timers mirrors Intl inside the sandbox, so a newly constructed instance no longer resolves to the prototype-level stub.

The tests are updated to replace the Intl.DateTimeFormat constructor via sinon.replace() (the ticket's suggested sinon.stub( Intl, 'DateTimeFormat' ) throws against the mirrored Intl), and to restore the sandbox at the end of each test to match the convention used elsewhere in the file. No production code is changed.

Testing: npm run grunt qunit:compiled reports 535/535 passing (0 failed) on both compiled.html and index.html. Before the change, the four documented getTimeZone assertions fail.

Trac ticket: https://core.trac.wordpress.org/ticket/64228

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Analysing the sinon major-version breaking changes and the @sinonjs/fake-timers Intl mirroring behaviour, drafting the dependency update and the test adjustments, and running the QUnit suite. All changes were reviewed, tested, and are owned by me.

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