Movement Speed Attribute Does Not Persist After Leaving and Rejoining the World

Description

When changing the movement speed attribute and then leaving and rejoining the world, the player’s movement speed resets to its default value.

This issue also applies to attribute modifiers. Any modifier applied to the minecraft:movement_speed attribute is not preserved. After the player dies, the attribute modification is completely removed and the movement speed returns to its default value.

Steps to Reproduce

1. Run:
   attribute @p minecraft:movement_speed base set 15

2. Exit the world

3. Rejoin the world

4. Run:
   attribute @p minecraft:movement_speed base get