Nested Collections ignore editorial_workflow when deleting a file.

**Describe the bug**
Using `editorial_workflow: true`, a pull request is created when a post is added or edited. But if you delete a post it doesn't generate a PR for the deletion, it just deletes and commits to `main`.

**To Reproduce**
Add a new post. Merge the PR. Then delete the post.

**Expected behavior**
A PR is generated in which the post is deleted.

**Actual behavior**
A commit on `main` is generated in which the post is deleted.

**Applicable Versions:**

- Netlify CMS version: netlify-cms-app 2.14.29, netlify-cms-core 2.38.7, netlify-cms 2.10.99
- Git provider: GitHub
- OS: macOS
- Browser version Chrome 88

**CMS configuration**

```yaml
backend:
name: git-gateway
branch: main
collections:
- name: posts
label: Post
folder: src/posts
create: true
fields:
- label: Title
name: title
widget: string
- label: Body
name: body
widget: markdown
```