Notification gives incorrect info about missing entry in archive-metadata.md

[hofmannc]

Testserver: qa keeper
Browser: firefox 77.0.1 (64-Bit) Chrome 83.0.4103.61
Version: Seafile 7.1.3

Action: Fill out archive-metadate.md completely-> save -> delete entry for "year" -> "archive" -> Warning: "field "Year is invalid or empty"

Observation: -> "notifications" -> shows wrong error for creation of certificate: in fact "year" is empty and CCBY is entered in "Licence"