Summary:
Teleporting via "/execute" to Nether/Overworld to tamed pets (allay, cats, dogs) creates a portal and teleports pets into it.
For example, you teleport using "/execute" to Overworld from Nether to a place where there is a dog nearby - a portal is created and your pet is teleported into it (the pet does not change the dimension, it is already in Overworld).
This works both when teleporting from Nether to Overworld to pets, and from Overworld to Nether to pets.
Also, when teleporting from Nether and Overworld (near the pet) to the End, the pet is teleported to the obsidian platform.
This also affects spectator mode, where your pets should not teleport to you at all. I expect that teleporting via /execute shouldn't affect pets in any way, since regular /tp teleportation doesn't teleport pets.
This breaks my test world and could potentially break other worlds.

Steps to reproduce:

1. Create a new world with cheats enabled.
2. Summon a dog and tame.
3. Switch to spectator mode
   //so you don't get teleported back to the nether - optional

4. /execute in nether run tp ~ ~ ~

   //the dog stays in overworld, the portal is not created

5. /execute in overworld run tp ~ ~ ~

Observed results:
After returning to overworld, a portal is created and the pet teleports into it.

Expected results:
After teleporting to the overworld, a portal is not created, and pets are not teleported.