update PyNaCl minimum version dependency

[rishitkhare]

Summary

PyNaCl's nacl.secret.Aead class was only added to PyNaCl in version 1.5. This commit updates the pyproject.toml to ensure that the version is 1.5 since voice_client.py is dependent on this class.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)