OpenXR Quest 3 VSync Not Honored

### Tested versions

4.2 Stable

### System information

Oculus Quest 3 Vulcan

### Issue description

When running my games on the Quest 3 using OpenXR and forward_plus, disabling VSync isn't honored, resulting in anywhere from mild to massive flicker. The game still runs, but it's not very pleasant. This happens if I disable VSync from the projects settings or though GDScript. The Android log issues this warning:

```USER WARNING: The requested V-Sync mode Disabled is not available. Falling back to V-Sync mode Enabled.```

### Steps to reproduce

Create any minimal OpenXR project, and disable vsync.

### Minimal reproduction project (MRP)

N/A