devices: ignore .incus-mounts in GetDevices

[siretart]

In Incus containers, /dev/.incus-mounts is created with mode 0700. Calling devices.GetDevices("/dev") fails with:

open /dev/.incus-mounts: permission denied

Similar to the existing .lxc and .lxd-mounts entries, .incus-mounts should be skipped during directory traversal:

diff --git a/devices/device_unix.go b/devices/device_unix.go
index bd401d3..174979d 100644
--- a/devices/device_unix.go
+++ b/devices/device_unix.go
@@ -100,7 +100,8 @@ func GetDevices(path string) ([]*config.Device, error) {
 			switch f.Name() {
 			// ".lxc" & ".lxd-mounts" added to address https://github.com/lxc/lxd/issues/2825
 			// ".udev" added to address https://github.com/opencontainers/runc/issues/2093
-			case "pts", "shm", "fd", "mqueue", ".lxc", ".lxd-mounts", ".udev":
+			// ".incus-mounts" added for Incus container environments
+			case "pts", "shm", "fd", "mqueue", ".lxc", ".lxd-mounts", ".udev", ".incus-mounts":
 				continue
 			default:
 				sub, err := GetDevices(filepath.Join(path, f.Name()))