Allow the spells to span midnight

[tidoust]

The spec-prod action may need a couple of minutes between the time it computes the publication date, generates the spec for publication, and the time it submits it to Echidna. In the meantime, a day may end, and a whole new day may start. Unfortunately, the automation spells break at the stroke of midnight, because "The publication date of this document must be set to today (UTC)".

One example at https://github.com/w3c/webcodecs/actions/runs/8335174561/job/22810156792

Not a major issue for sure but I'm wondering whether we could relax the rule slightly to allow publications with yesterday's date within, say, 10mn of midnight UTC.

Via w3c/webcodecs#782