Steps to Reproduce:
Type the following command in chat `/attribute @s minecraft:generic.movement_speed base set 0.2`

Observed Results:
You'll be about twice as fast when walking around, but slowed to normal speed if you jump into the air. Conversely, if you do `/attribute @s minecraft:generic.movement_speed base set 0.03`, your ground movement will be very sluggish, but you'll still be able to have normal speed if you jump.

Expected Results:
The ground speed and air speed would be affected equally. (i.e. doubling ground speed would also double airspeed)