nb-tabset not workign with ng-content

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
I want an add-on over nb-tabset. I add tabs from the parent component. nb-tabset is empty. How to fix it?

**Expected behavior:**
nb-tabset working with ng-content.

**Steps to reproduce:**
1. Create component with nb-tabset -> ng-content
2. Use this component as child component with ng-tab inside.
3. nb-tabset is empty

**Related code:**

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```

test content

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### Other information:

**npm, node, OS, Browser**
node 18.16.0
npm 9.5.1
angular 15.2.9
nebular 11.0.0