Player's OnGround tag doesn't update when riding a vehicle

When riding a vehicle, the OnGround tag doesn't update.

How to reproduce:

1. Summon a pig and place a saddle on it.

2. While flying in the air, execute the following command:

   /data get entity @s OnGround

   → ✔ The tag is set to false (0b).

3. Ride the pig without touching the ground.

4. Execute the command from step 2 again.
   → ✔ The tag is set to false (0b).

5. Dismount the pig.

6. While on the ground, execute the command from step 2 again.
   → ✔ The tag is set to true (1b).

7. Ride the pig again.

8. Execute the command from step 2 again.
   → ❌ The tag is set to true (1b).

Expected result:

The OnGround tag would always be false while riding an entity, like in previous versions.

Observed result:

The OnGround tag keeps its value from before riding an entity, which sometimes makes it inaccurate.