TNSNativeSource gets duplicated in Xcode projects #5765

Issue Description

Starting with NativeScript v8.6.0, ns prepare ios may duplicate native code section TNSNativeSource in Xcode projects.

In particular, this seems to be related to this PR: NativeScript/nativescript-dev-xcode#15

Reproduction

Download the file to ~/Downloads folder: extra.zip

1. ns create testApp --js
2. cd testApp
3. ns platform add ios
4. cd App_Resources/iOS
5. mkdir src
6. cd src
7. cp ~/Downloads/extra.zip .
8. unzip extra.zip
9. rm extra.zip
10. cd ../../..
11. ns prepare ios
12. touch App_Resources/iOS/src/extra.m
13. ns prepare ios
14. open platforms/ios/testApp.xcodeproj

Relevant log output (if applicable)

Environment

No response

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