Updating to 1.21.4 has no biome blending applied, sometimes causing straight biome borders at chunk borders.

How to reproduce

1. Set render distance to 2 chunks
2. In 1.21.3: create a new world
   • Creative
   • Seed: 60694719
   • Keep winter drop experiment disabled
3. Don't move and exit the game
4. Update to 1.21.4-pre3
5. Reenter the world
6. Increase render distance and look north-east
7. The biome border is straight

Expected result
The biomes are blended causing non-straight border.

Cause
The data-fixes apply the BlendingDataFix in schema 3441 (first snapshot of 1.20), but it isn't applied in the 1.21.3 -> 1.21.4 update.