Improve Norwegian names of the Sámi National Day

Based on recommendations from Språkrådet
https://www.sprakradet.no/svardatabase/sporsmal-og-svar/samenes-nasjonaldag/
and the Sámi Parliament of Norway
https://sametinget.no/om-sametinget/nasjonaldag-og-nasjonale-symboler/

The names also correspond to the names used
on the Norwegian Bokmål and Norwegian Nynorsk
Wikipedia pages for the Sámi National Day.