Plugin: Fix building plugin zip to include interactive blocks

[gziolo]

What?

Fixes the issue reported in the #50041 (comment):

Version 15.9.20230511 returns 404 for the following files:

vendors.min.js
interactivity.min.js
navigation.min.js

Why?

Files were missing in the gutenberg.zip file.

How?

Testing Instructions

Run npm run build:plugin-zip locally (warning: it removes all artifacts from the branch) or check one of the CI job in this branch that should have the zip file attached.

I uploaded the gutenberg.zip file to a WordPress instance and ensured that the Navigation block works correctly with the feature flag enabled:

Basically, we have to ensure that the Navigation block, the navigation submenu, and the page list behave exactly the same when the option is activated/deactivated. I used the testing instructions from #50041:

Toggle the Experimental option in Gutenberg -> Experiments:

• Check that the mentioned experiences (and anything not mentioned) work as expected.
• Check that it is only sending the Interactivity API scripts.
• Change the settings of the navigation block to ensure it works fine in all cases.
• If the Overlay menu is set to off and the "Show arrow" is set to false, the scripts shouldn't be loaded.

[gziolo]

@fabiankaegy, we must backport this bug fix to the Gutenberg 15.8 RC.

[fabiankaegy]

I just cherry-picked this PR to the release/15.8 branch to get it included in the next release: 4871f27