The favicon validation error message is now more specific:
Before: "favicon must be one or two emoji — no markup"
After: "favicon must be the literal emoji character(s) — not an HTML entity, quoted string, or markup (send 📊, not '📊' or '<svg/>')"
Evidence
Favicon validator (search for "favicon must be the literal emoji character(s)")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.