[Bug] gz_x500_gimbal: gimbal_device_attitude_status reports large roll/yaw when commanding pitch = -90°

[haojiahuo123]

Describe the bug

Describe the bug
In Gazebo (gz) simulation make px4_sitl gz_x500_gimbal, when I command the gimbal to point straight down (pitch = -90°), the reported gimbal_device_attitude_status shows pitch close to -90° but also shows a large roll and yaw angle. This happens consistently across repeated tests.
This is problematic because users may rely on gimbal_device_attitude_status (or the printed Euler angles derived from it) to understand and control the gimbal attitude.

Expected behavior
gimbal_device_attitude_status.q should remain correct and consistent. If the PX4 console prints Euler angles derived from the quaternion, the printed angles should be chosen in a way that is continuous and not misleading near pitch = ±90° (e.g., avoid large roll/yaw jumps for essentially the same attitude).

Actual behavior
After sending pitch = -90°, the reported attitude is stable but includes large roll and yaw values:
TOPIC: gimbal_device_attitude_status
gimbal_device_attitude_status
timestamp: 737172000 (0.036000 seconds ago)

q: [-0.50009, -0.49912, 0.50071, -0.50009] **(Roll: -77.8 deg, Pitch: -89.9 deg, Yaw: 167.7 deg)**
failure_flags: 0
delta_yaw: 0.00000
delta_yaw_velocity: 0.00000
device_flags: 64 (0b100'0000)
target_system: 0
target_component: 0
gimbal_device_id: 0
received_from_mavlink: False

Steps to reproduce

1. Start SITL:
   make px4_sitl gz_x500_gimbal
2. Configure gimbal for v2 control (default gimbal manager workflow).
3. Use pymavlink to send gimbal manager commands. Send MAV_CMD_DO_GIMBAL_MANAGER_PITCHYAW with:
   pitch=-90 deg, yaw=0 deg
4. Observe:
   listener gimbal_device_attitude_status

Flight Log / Additional Information

PX4 version: 1.17.0
PX4 git-branch: main
Gazebo version:Gazebo Sim, version 8.10.0
Operating System:Ubuntu 22.04 LTS