Connection: fix the connected plugins option on multisites

[sergeymitr]

Proposed changes:

Recent optimizations of the connected plugin options update/sync exposed an issue in the original implementation made in #17908, making the "active connected plugins" option always empty on multisites.
Here we fix that problem.

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

p1725991000681419-slack-CDLH4C1UZ
https://github.com/Automattic/jetpack-marketing/issues/976

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

No.

Testing instructions:

1. Create a new multisite, create a couple of subsites.
2. Switch Jetpack Beta to the branch, activate Jetpack, connect it. Confirm Jetpack Debug shows Jetpack in "Jetpack Plugins" card.
3. Try the same on another subsite with another set of Jetpack plugins, confirm the plugins show up the same way.

[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/connected-plugins-on-multisites 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 fix/connected-plugins-on-multisites
  

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/connected-plugins-on-multisites
  

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, ...).
  
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• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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