User can alter typography of block placeholder in the navigation block

[talldan]

Step-by-step reproduction instructions

1. Add a navigation block and select it
2. Select some typography options like font weight and strikethrough

Expected behaviour

The placeholder is not affected
-- or --
The typography options are not visible while the placeholder is shown

Actual behaviour

The user can adjust the typography of the placeholder (fortunately not font size)

Screenshots or screen recording (optional)

WordPress information

• WordPress version: 5.7
• Gutenberg version: 10.2

[jasmussen]

Fix in #30011