Sync python-send-email with the updated tutorial - #873

Syncs python-send-email/ with the maintenance update of Sending Emails With Python.

What changed

• Added sendgrid_example.py, the SendGrid example from the article, with the fixed error handler (print(str(e)) instead of print(e.message), which raised AttributeError on Python 3).
• Pinned the article's dependencies in pyproject.toml to match the article's dependencies field: aiosmtpd==1.4.6, yagmail[all]==0.16.0, proton-mail-bridge-client==1.0.1, sendgrid==6.12.5. Regenerated requirements.txt (uv pip compile) and uv.lock.

Links

• Article draft (admin): https://realpython.com/pbjt/blog/post/2454/change/
• Maintenance card: https://trello.com/c/YcA1tIBc

Verification

• Fresh Python 3.12 venv from requirements.txt.
• Ran every stdlib script (plain text, HTML, attachment, reply-to, multiple recipients, address, CSV) against a local aiosmtpd server on port 8025. All exited cleanly.
• sendgrid_example.py without an API key prints HTTP Error 401: Unauthorized instead of crashing.
• Imported yagmail (0.16.0), proton_mail_bridge_client, and sendgrid, and compiled the Yagmail and Proton examples. Sending through them needs real credentials, so they weren't run end to end.
• ruff@0.14.1 format --check and ruff@0.14.1 check both pass.

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