Plugin sidebar no longer pinned by default

[IreneStr]

Describe the bug
Up until 10 days ago, the Yoast SEO sitebar was pinned automatically on activation. While the implementation on our side is unchanged, this is no longer the case.

To reproduce
Steps to reproduce the behavior:

1. Checkout the Gutenberg master branch.
2. Activate Gutenberg.
3. Install and activate Yoast SEO 13.5.
4. Start creating a new post in an incognito browser (to make sure all settings are default)
   You see that Yoast is not pinned anymore:

5. Click Tools and see that Yoast appears in Plugin section:

6. Click Yoast, and you get Yoast sidebar, but it is still not pinned in the toolbar:

7. Click to pin ("star") on top, then you get Yoast sidebar pinned in the toolbar:

Expected behavior
Plugin sidebars to be pinned by default on activation.

Screenshots
See above

Editor version (please complete the following information):

• WordPress version: 5.4
• Does the website has Gutenberg plugin installed, or is it using the block editor that comes by default? Gutenberg plugin
• If the Gutenberg plugin is installed, which version is it? master

Desktop:

• OS: independent of OS
• Browser: all browsers
• Version: N/A

Smartphone:

• Device: independent of device
• OS: independent of OS
• Browser: all browsers
• Version: N/A

Additional context

• @afercia pinpointed this PR as the likely culprit: Add interface package with sidebar functionality #20698
• In the core editor chat of April 15, it was confirmed by @gziolo that this is a bug in the Gutenberg and the implementation on our side (see above) is correct.

[afercia]

See also #21506

[manooweb]

Hello,
I reproduce the same issue with our Polylang Pro plugin sidebar and Gutenberg 7.9.0 installed.
No issue with Gutenberg 7.8.1 or WP 5.4 only.
Regards