WP.com: allow enabling React 19 GB experiment via sticker

[simison]

Proposed changes

• Enables the gutenberg-react-19 Gutenberg experiment (shipped in GB 23.4.0) for sites with the gutenberg-react-19 blog sticker.

Related product discussion/links

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

Testing instructions

• Have Atomic dev site (internal ref PCYsg-Osp-p2, not a regular Atomic site)
• Enable sticker on Atomic site via CLI or RC using 163051-ghe-Automattic/missioncontrol
• Apply PR e.g. using Jetpack beta plugin
  

[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 WoA dev 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 (WordPress.com Site Helper), and enable the update/gutenberg-react-19-experiment-toggle branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin update/gutenberg-react-19-experiment-toggle

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 Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ 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 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/jetpack-mu-wpcom/src/class-jetpack-mu-wpcom.php	29/427 (6.79%)	-0.13%	8 💔

Full summary · PHP report · JS report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}