TASK: Add a `flip_coin()` method

[TheGittyPerson]

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Difficulty: Upper beginner

TODO:

• Add the method to the Person class in person.py
• Remember to add type hints and docstrings where necessary and follow PEP 8

PR steps:

1. Fork this repo
2. Clone the forked repo
3. Create a new branch and name it feature/flip-coin-method
4. Push commits to your remote fork
5. Create a pull request titled TASK: Add a `flip_coin()` method (#149)
6. At the end of the PR description, add Closes #149
7. Submit the PR (Ensure you allow maintainers to edit)

Please make sure you have read the Contributing Guidelines before working.

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