GM: Cruise Fault at standstill

### Describe the bug

Some cases, where I like to use stock ACC or OpenPilot ACC to hold my brake at a stop light, occasionally would trigger Cruise Faulted red alert.

I am able to replicate this on master, master-ci and other forks as well. Happens both on stock and op ACC.


### Which car does this affect?

2020 GMC Sierra 1500

### Provide a route where the issue occurs

dc7716b32bf25574|2023-12-22--21-09-03--5

### openpilot version

0.9.6

### Additional info

_No response_

Begin with the supplied route dc7716b32bf25574|2023-12-22--21-09-03--5 and the 2020 GMC Sierra 1500 context, comparing stock ACC and openpilot ACC behavior at a standstill. Trace the relevant cruise-fault handling and CAN/DBC data, then verify that the reproduced route no longer produces a false Cruise Faulted alert.

Written by the indexing model from the issue text.