Enforce SMTPUTF8 policy

[Psych0meter]

The bot encountered this kind of error when processing emails containing non-ASCII characters (e.g., accents or special symbols):

UnicodeEncodeError: 'ascii' codec can't encode character '\xe0' in position 4: ordinal not in range(128)

Dump example :

{
    "__type": "Event",
    "extra.doc_count": 380,
    "extra.subject": "Merci \u00e0 tous pour cette ann\u00e9e GiGA exceptionnelle \u2013 cap sur 2025 ! (raw: Merci =?utf-8?Q?=C3=A0?= tous pour cette =?utf-8?Q?ann=C3=A9e?= GiGA exceptionnelle =?utf-8?Q?=E2=80)",
    "feed.accuracy": 100.0,
    "feed.name": "xxx",
    "feed.provider": "xxx",
    "raw": "xxx",
    "time.observation": "2024-12-23T20:53:35.319135+00:00"
}

[sebix]

Thank you for the fix! I'll look into it, hopefully this weekend.

If the CI tests fail, it's likely not because of your changes.