Having sneaking_speed attribute as 0.8 or higher allowed players to sprint while sneaking in previous versions, like in 1.21.3 (Independent of MC-152728, you can start sprinting while sneaking in this case)
Probably due to the fix of MC-152728.
Not sure if this change is intentional, as this change wasn't documented.

How to reproduce:

1. In 1.21.3, set your sneaking_speed attribute to 0.8 or higher:

   /attribute @s sneaking_speed base set 0.8

2. Try to sprint while sneaking (Do not sprint before sneaking, this will cause MC-152728).
3. Repeat step 1~2 but in version 24w46a.

You can also use a predicate to check if the player is sprinting, using this command below (in a repeating command block):

/execute as @p if predicate {"condition":"minecraft:entity_properties","entity":"this","predicate":{"type":"minecraft:player","flags":{"is_sprinting":true}}} run say SPRINTING