Update n_queens.cpp

[ZohaiAli]

i update your code because it has some error please accept this code

Description of Change

Checklist

• [x] Added description of change
• [ ] Added file name matches File name guidelines
• [ ] Added tests and example, test must pass
• [ ] Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• [ ] Relevant documentation/comments is changed or added
• [x] PR title follows semantic commit guidelines
• [ ] Search previous suggestions before making a new one, as yours may be a duplicate.
• [ ] I acknowledge that all my contributions will be made under the project's license.

Notes: