fix the download URL for mbtiles file

the URLs below are dead:

• https://mbtiles.top/planet/Combined.mbtiles
• https://osm.dbtc.link/mbtiles/2023-05-29-planet.mbtiles.lz4

the new URL is:

• https://osm.dbtc.link/mbtiles/2025-03-28-planet.mbtiles

Issue: cortext/operations/cortext-env#48