In 5.8 RC2 on new block widgets screen JS error appears for the text widget

[exstheme]

Description

In 5.8 RC2 on new block widgets screen JS error appears for the text widget:
Error message:

The "text" block was affected by errors and may not function properly. Check the developer tools for more details.

Console error:

widgets.js?ver=5ee29b11357eb747d08e2a33c8307fa7:763 TypeError: wp.editor.initialize is not a function
    at buildEditor (text-widgets.js?ver=5.8-RC2:265)
    at n.initializeEditor (text-widgets.js?ver=5.8-RC2:359)
    at renderWhenAnimationDone (text-widgets.js?ver=5.8-RC2:434)
    at HTMLDocument.handleWidgetAdded (text-widgets.js?ver=5.8-RC2:437)
    at HTMLDocument.dispatch (jquery.js?ver=3.5.1:5430)
    at HTMLDocument.elemData.handle (jquery.js?ver=3.5.1:5234)
    at Object.trigger (jquery.js?ver=3.5.1:8719)
    at HTMLDocument.<anonymous> (jquery.js?ver=3.5.1:8797)
    at Function.each (jquery.js?ver=3.5.1:385)
    at jQuery.fn.init.each (jquery.js?ver=3.5.1:207)

Step-by-step reproduction instructions

1. Install starter content on version 5.7
2. Update WordPress to 5.8 RC2 with beta tester plugin
3. Go to Appearance -> Widgets

Expected behaviour

Working without errors.

Actual behaviour

Error message and console error appears.

Screenshots or screen recording (optional)

https://i.imgur.com/TjJfIqL.png

WordPress information

• WordPress version: 5.8 RC2
• Gutenberg version: Not installed - Default used
• Are all plugins except Gutenberg deactivated? Yes
• Are you using a default theme (e.g. Twenty Twenty-One)? No

Device information

• Device: Desktop
• Operating system: Linux Mint 20
• Browser: Chromium v90

[kevin940726]

It's likely a duplicate of #33203 and should already been fixed.