fix(plugin-nested-docs): corrects data shape of breadcrumbs returned in hooks (#10866)

### What?
The `plugin-nested-docs` returns an array of breadcrumbs - the
`resaveChildren` file accidentally processed the breadcrumbs twice, once
where the data is updated and once within the `populateBreadcrumbs`
function which was causing the objects to be double nested.

### How?
Removes the extra nesting from `resaveChildren` file and allows the
`populateBreadcrumbs` to return the final data.

Fixes #10855

packages/plugin-nested-docs/src/hooks/resaveChildren.ts

@@ -81,10 +81,7 @@ const resave = async ({ collection, doc, draft, pluginConfig, req }: ResaveArgs)
           await req.payload.update({
             id: child.id,
             collection: collection.slug,
-            data: {
-              ...child,
-              [breadcrumbSlug]: await populateBreadcrumbs(req, pluginConfig, collection, child),
-            },
+            data: populateBreadcrumbs(req, pluginConfig, collection, child),
             depth: 0,
             draft: isDraft,
             locale: req.locale,