The 25w03a changelog article mentions the weather test environment definition which is actually raining in the test_environment_definition_type registry.
How to reproduce:
Create a test environment:
{ "type": "minecraft:weather", "weather": "rain" }Try entering the world.
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.
Please attach a datapack that can be used to reproduce the issue