The 25w03a changelog article mentions the weather test environment definition which is actually raining in the test_environment_definition_type registry.

How to reproduce:

1. Create a test environment:

   {
     "type": "minecraft:weather",
     "weather": "rain"
   }
   

2. Try entering the world.
3. Observe the error in the console: 

   Unknown registry key in ResourceKey[minecraft:root / minecraft:test_environment_definition_type]: minecraft:weather
   

Possible solution:
Rename the minecraft:raining test environment definition type to minecraft:weather.