Siege Modification - Does Not Work In Tandem With Captain Rex Nebula

**Describe the bug**
I have Siege Modification on a creature. I used Captain Rex Nebula's ability to turn it into a Vehicle, but the "it's a creature" didn't trigger, and it didn't get +3/0 and I couldn't use it as a creature. The creature did not have summoning sickness.

**To Reproduce**
Steps to reproduce the behavior:
1. Attach Siege Modification to a creature.
2. Use Captain Rex Nebula to turn that creature into a vehicle.
3. Attempt to go to combat with creature.
4. Observe that you cannot declare it as an attacker.

**Expected behavior**
The nature of the aura should permit it to be usable as a creature when transformed into a vehicle.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
- OS: Windows 11