File widget ignores its own media_folder and instead uses media_folder from the root

[cshaa]

Describe the bug
My team is working on a static web page that has a lot of images that are preprocessed by Vite. That's why we have media_folder: "src/assets/uploads" in the root of the config (that's where images are supposed to go). Now, we want to add the option to upload files, which should be placed directly in the public folder, so we used the media_library.media_folder property on the file widget – but it is ignored, and the files are uploaded to src/assets/uploads instead of public/uploads.

To Reproduce

1. Create the following config.yml:

local_backend: false
backend:
  name: gitlab
  repo: ...
  branch: main
  auth_type: pkce
  api_root: https://gitlab.druit.org/api/v4
  base_url: https://gitlab.druit.org
  auth_endpoint: oauth/authorize
  app_id: ...
locale: cs
publish_mode: simple
media_folder: src/assets/uploads
public_folder: "#uploads"
collections:
  - ...
  - name: files
    label: Files
    folder: src/content/files
    create: true
    fields:
      - widget: file
        name: file
        media_library:
          allow_multiple: false
          media_folder: public/uploads

2. Go to administration > Files and uplad a file
3. See that it was uploaded to src/assets/uploads and not public/uploads

Applicable Versions:

• Decap CMS version: 3.4.0
• Git provider: GitLab

• Node.JS version: 23.3