Mongolian holidays observance verification

[PPsyrius]

From #2601

At the moment, there are two Mongolian WORKDAY observances tied to "week of the month" - which are:

• National Literary, Cultural and Book Days (Үндэсний бичиг соёл, номын өдрүүд): Saturday and Sunday in the 3rd week of May and September. (5 болон 9 дүгээр сарын гурав дахь долоо хоногийн Бямба, Ням гараг.), added on July 2nd, 2021
• Environmental Protection Days (Байгаль орчныг хамгаалах өдрүүд): 4th Week of September (9 дүгээр сарын дөрөв дэх долоо хоног)

References:

• (Mongolia's) Law on Public Holidays and Days of Observation
• 2004-2024 Wayback Machine Records

For the record, we've previously reached out to [email protected] for clarification but received no replies, thus these two observances remains unimplemented at the moment.