Player is unaffected by the gravity attribute modifier when in swim mode

Steps to Reproduce:

1. Enter a large body of water

2. Run the command: /attribute @s minecraft:gravity base set 10

3. Hold space to see that gravity is now stronger and won’t let you move in the vertical axis

4. Press the sprint key and move forwards to enter swim mode and move freely in the vertical axis

Observed Results:  

Player is unaffected by gravity when swimming

Expected Results:  

Gravity effects the player like in all circumstances (excluding Creative flight)