Fields with widget: hidden and default value does not work with collections containing files property

[andreasbalevik]

Describe the bug
Im using Netlify CMS with jekyll.

I got this problem.

A collection with files, using the widget hidden with a default value does not get populated.

  - label: "Pages [NO]"
    name: "pages_no"
    files:
      - label: "Frontpage"
        name: "frontpage_no"
        file: "_nb/pages/frontpage.md"
        fields:
          - {label: Layout, name: layout, widget: hidden, default: index }
          - {label: Language, name: language, widget: hidden, default: nb }
          - {label: Page Title, name: page_title, widget: string}

Outputs

frontpage.md

---
page_title: Test 123
---

But using a collections with folder.

- label: "Pages [folder]"
   create: true
   folder: "_folder"
   name: "page_folder"
   fields:
     - {label: Layout, name: layout, widget: hidden, default: index }
     - {label: Language, name: language, widget: hidden, default: en }
     - {label: Page Title, name: page_title, widget: string}

Outputs correct
{{slug}}.md

---
layout: index
language: en
page_title: Test 123
---

To Reproduce

Site with netlify cms. Use _config provided below.

Expected behavior

  - label: "Pages [NO]"
    name: "pages_no"
    files:
      - label: "Frontpage"
        name: "frontpage_no"
        file: "_nb/pages/frontpage.md"
        fields:
          - {label: Layout, name: layout, widget: hidden, default: index }
          - {label: Language, name: language, widget: hidden, default: nb }
          - {label: Page Title, name: page_title, widget: string}

should produce a the file
frontpage.md with the following content

---
layout: index  
language: nb 
page_title: Test 123
---

Applicable Versions:

netlify-cms-app 2.15.42
netlify-cms-core 2.49.0
netlify-cms 2.10.162

Github

CMS configuration

---
backend: 
  branch: main
  name: git-gateway

collections:

  # THIS DOES NOT WORK
  - label: "Pages [NO]"
    name: "pages_no"
    files:
      - label: "Frontpage"
        name: "frontpage_no"
        file: "_nb/pages/frontpage.md"
        fields:

          # DEFAULT VALUE DOES NOT WORK
          - {label: Layout, name: layout, widget: hidden, default: index }
          - {label: Language, name: language, widget: hidden, default: nb }
          - {label: Page Title, name: page_title, widget: string}

  # THIS DOES NOT WORK
  - label: "Pages [EN]"
    name: "pages_en"
    files:
      - label: "Frontpage"
        name: "frontpage_en"
        file: "_en/pages/frontpage.json"
        fields:

          # DEFAULT VALUE DOES NOT WORK
          - {label: Layout, name: layout, widget: hidden, default: index }
          - {label: Language, name: language, widget: hidden, default: en }
          - {label: Page Title, name: page_title, widget: string}

  # THIS WORKSS
  - label: "Pages [folder]"
    create: true
    folder: "_folder"
    name: "page_folder"
    fields:
      - {label: Layout, name: layout, widget: hidden, default: index }
      - {label: Language, name: language, widget: hidden, default: en }
      - {label: Page Title, name: page_title, widget: string}

media_folder: static/images/uploads

[erezrokah]

Closing this in favor of #3046, thank @andreasbalevik