Bug description

IMip invitations sent by Nextcloud must set charset to UTF-8 as the attendees may use UTF-8 characters.

See https://www.rfc-editor.org/rfc/rfc6047.html#section-2.4

Steps to reproduce

1. Create a user like OC_PASS=jose occ user:add --display-name "José" --password-from-env jose; occ user:setting jose settings email [email protected]
2. Invite José to an event
3. See a iconv warning in the mail app

Expected behavior

The content-type header needs to contain charset=UTF-8

Nextcloud Server version

master, but applies to older versions too.

Additional info

No response