Changing world difficulty does not update firing speed of existing skeletons

If you change the difficulty from either Easy or Normal to Hard, skeleton variants will continue to have a fire rate of 3 seconds, instead of 2. Relogging fixes the issue.

Steps to Reproduce:

1. Set world difficulty to Easy, or Normal
2. Summon a skeleton, or skeleton variant
3. Allow it to shoot arrows at you (Observe fire rate)
   ^{(for ease of testing)}

   /effect give @p minecraft:regeneration infinite 127 true
   

4. Change difficulty to Hard
5. Repeat step 3

Observed & Expected Results:

- The skeleton fire rate remains consistent across difficulties.
- The fire rate should properly update to a quicker, or slower speed depending on what the current difficulty is.

Screenshots/Videos:

24w07a.mp4