Write: fix publish status message for existing drafts

[kbrown9]

Fixes RSM-2439

Proposed changes

• Fix isUpdate flag in savePost() to check the current post status (state.postStatus) instead of the target status (postStatus parameter).
• This corrects the status message when publishing an existing draft — it now shows "Publishing…" / "Published!" instead of "Updating…" / "Updated!".

Related product discussion/links

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

No.

Testing instructions

1. Create a new post and save it as a draft (or use an existing draft post).
2. Open the draft in the Write editor: wp-admin/admin.php?page=write&post={id}
3. Click the Publish button.
4. Before fix: Status message flashes "Updating…" then "Updated!".
5. After fix: Status message flashes "Publishing…" then "Published!".
6. Also verify that updating an already published post still shows "Updating…" / "Updated!".

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

[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/write_publish_button branch.
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bin/jetpack-downloader test jetpack-mu-wpcom-plugin update/write_publish_button

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[github-actions]

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Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report