mail/py-resend: Update to 2.29.0

While here, switch to use USE_PYTHON=pep517.

Changelog:

• https://github.com/resend/resend-python/releases/tag/v2.28.0
• https://github.com/resend/resend-python/releases/tag/v2.28.1
• https://github.com/resend/resend-python/releases/tag/v2.29.0

Reported by: portscout