Description

Custom template configuration in experimental-theme.json file does not work neither in default themes nor in custom ones.

Step-by-step reproduction instructions

1. Create my-custom-template.html file within current active theme's "block-templates" folder
2. Add configuration from Code snippet part to active theme's experimental-theme.json file
3. Go to admin panel and go to "Posts -> Add New"
4. In the opened screen open "Template dropdown"

Expected behaviour

1. Template dropdown should not contain above mentioned my-custom-template as an option because it should not be available for any post type but page.
2. The template name must be read as The template title instead of my-custom-template based on experimental-theme.json file configuration

Actual behaviour

1. Template is available in all post types: postTypes restriction does not work
2. Template name is read as my-custom-template instead of The template title

Screenshots or screen recording (optional)

Code snippet (optional)

...
"customTemplates": [
    {
      "name": "my-custom-template",
      "title": "The template title",
      "postTypes": [
        "page"
      ]
    }
  ]
...

WordPress information

• WordPress version: 5.7.1
• Gutenberg version: 10.5.4
• 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: Windows 10
• Browser: Chrome 90.0.4430.93 (Official Build) (64-bit)