Code coverage: Fix warnings in scheduled updates package

[tbradsha]

When running code coverage tests on scheduled-updates, we get 34 warnings due to errant @covers annotations. This PR corrects those.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
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Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

Check the CI Tests → Code Coverage run. On trunk it looks like this:
https://github.com/Automattic/jetpack/actions/runs/12717372492/job/35453699359#step:10:8096

With this branch the warnings should be gone.

[github-actions]

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[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the fix/scheduled-updates/coverage_warnings branch.

  • For jetpack-mu-wpcom changes, also add define( 'JETPACK_MU_WPCOM_LOAD_VIA_BETA_PLUGIN', true ); to your wp-config.php file.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/scheduled-updates/coverage_warnings
  

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[anomiex]

LGTM, and the test output has no warnings about @covers anymore.