Fix: nested + i18n customPath issue

[demshy]

Summary

Addressing #7389

When using nested collection combined with i18n, we encountered a bug, where instead of saving content, we would get empty commits. This did not happen when using local backend via proxy.
After inspecting exactly what happens in the backend implementation I figured out that the problem actually happens in backend.ts when it sets the newPath property as if the file was being renamed every time the customPath is set. This way the updateTree function in the API.ts goes into another mode, loops the i18n files and eventually updates the tree with existing blob IDS instead of the newly uploaded ones.
Added a condition where newPath is passed on only if it differs from the currentPath - so only in case the file is actually being moved.

Test plan

local_backend: true

backend:
  name: git-gateway
  branch: decap-debug
  squash_merges: true

display_url: https://hugo-template.netlify.app/
logo_url: /media/brand/logo.svg
media_folder: static/media/uploads
public_folder: /media/uploads

i18n:
  structure: multiple_files
  locales: [en, sl]

slug:
  encoding: ascii
  clean_accents: true

collections:
  - label: 'subfolders'
    name: 'subfolders'
    folder: 'content/subfolders'
    identifier_field: 'title'
    create: true
    i18n: true
    extension: 'md'
    meta: { path: { widget: string, label: 'Path', index_file: 'index' } }
    nested:
      depth: 10
      subfolders: true
      summary: '{{title}}'
    fields:
      - { label: 'Title', name: 'title', widget: 'string', i18n: true }

Directory structure

subfolders
└── management
    ├── index.en.md
    ├── index.sl.md
    └── nested
        └── index.en.md

When editing the nested entry using Github gateway it will no longer result in an empty commit instead of crating the index.sl.md file.

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