Blaze: avoid errors when post type label is not available

[jeherve]

Fixes #31591

Proposed changes:

Follow-up from #31399. In some scenarios (like after the post publication for some reason), the post type label isn't immediately available. Let's set a default to avoid that, even if that default will actually never really be shown since the panel is not displayed when the post is already published.

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

• N/A

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

• No

Testing instructions:

On a connected Jetpack site:

• Go to Posts > All Posts
• Click on a post that is already published to enter the block editor.
• See no errors when the editor is finished loading.

[github-actions]

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Jetpack plugin:

• Next scheduled release: July 5, 2023.
• Scheduled code freeze: June 26, 2023.

[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 plugin. Once the plugin is active, go to Jetpack > Jetpack Beta > Jetpack and enable the fix/error-post-type-label-blaze branch.

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

  bin/jetpack-downloader test jetpack fix/error-post-type-label-blaze
  

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[samiff]

Thanks for the quick fix!

[samiff]

cherry-picked to the 12.3-beta