Heading level dropdown missing icons and text

[dcalhoun]

Description

After inserting a Heading block, the toolbar button does not display an icon.
Also, after opening the heading level dropdown, the level icons and text are
missing.

This regression appears to have been introduced through #46003.

Step-by-step reproduction instructions

1. Add a Heading block to a post.
2. In the toolbar above the keyboard, note the heading level button does not
   display an icon.
3. Tap the heading level button.

Expected behaviour

The heading level dropdown displays a list of buttons with an icon and label for
each heading level.

Actual behaviour

The heading level dropdown displays an list of empty buttons.

Screenshots or screen recording (optional)

Toolbar Button	Dropdown List

WordPress information

• WordPress version: 6.2.2
• Gutenberg version: 16.0.0
• Are all plugins except Gutenberg deactivated? Yes
• Are you using a default theme (e.g. Twenty Twenty-One)?
  Yes

Device information

• Device: iPhone 13 mini
• Operating system: iOS 16.5.1
• WordPress app version: 22.7.0.0