Fix multiple scheduled update sync issue

[zaerl]

Fixes sync issues in the wpcom/v2/update-schedules endpoints.

Proposed changes:

• Add the jetpack_scheduled_plugins_update_sync filter that can prevent updating jetpack_scheduled_plugins_update option
• Block sync during the delete phase found in WPCOM_REST_API_V2_Endpoint_Update_Schedules::update_item

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?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

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

No.

Testing instructions:

• Install fix/su-multiple-sync-issue in WordPress.com Features
• Be sure to have needed jobs sandboxed and the watcher running
• Add the code found in pcmemI-2Ww-p2 at "Monitoring Jetpack syncs" section
• Leave tail -f -n 40 /tmp/php-errors open

On https://wordpress.com/plugins/scheduled-updates/__BLOG__

1. Create a scheduled update.
2. Update it without changing plugins.
3. Delete it.
4. Add other scheduled updates.
5. Change plugins.
6. Etc.

The jetpack_scheduled_plugins_update string should appear three times in your logs. Perform other tests. The sync count should always be:

1. Read: 0
2. Create: +1
3. Update: +1
4. Delete: +1

Ensure the is always on sync using wpsh:

switch_to_blog(__BLOG_ID__);
print_r( get_option('jetpack_scheduled_plugins_update') );

[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/su-multiple-sync-issue 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/su-multiple-sync-issue
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add testing instructions.
  
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• ✅ Add changelog entries to affected projects
  

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[TimBroddin]

Awesome work!

[obenland]

@zaerl Let's add hook docs to this for future reference.

How would you feel about using the hook string directly rather than abstracting it into a constant?
Feels to me like an opportunity to improve readability and debug-ability over DRY-ness.