test-virgl-qemu.sh: switch to blob=true for QEMU \u22658.0

QEMU \u22658.0 dropped the legacy 'virgl=on' device property in favour of
the more general 'blob=true' which enables the VIRTIO_GPU_F_RESOURCE_BLOB
feature negotiated by the redox-drm virtio backend. Without this,
the device property was silently dropped and the guest received
2D-only KMS without any 3D acceleration.

The new 'blob=true' activates the virgl blob-resource path, matching
the VIRTIO_GPU_F_RESOURCE_BLOB bit that redox-drm already negotiates
on the host-guest boundary.

local/scripts/test-virgl-qemu.sh

@@ -97,16 +97,16 @@ fi
 
 # Build the QEMU command.
 # Crucial: virtio-vga-gl (NOT virtio-gpu/virtio-vga) is the 3D-capable device.
-#   -device virtio-vga-gl,virgl=on : required for host->guest 3D
-#   -display gtk,gl=on              : host exposes EGL surface
-#   -machine q35                    : modern Intel chipset (default in our scripts)
+# QEMU ≥ 8.0 dropped the legacy `virgl=on` property; `blob=true` is the
+# modern equivalent and activates the virgl blob-resource path the
+# redox-drm backend negotiates via VIRTIO_GPU_F_RESOURCE_BLOB.
 qemu_cmd=(
     qemu-system-x86_64
     -machine q35
     -smp "${smp_count}"
     -m "${ram_mb}"
     -drive file="${img_path}",format=raw,if=virtio
-    -device virtio-vga-gl,virgl=on
+    -device virtio-vga-gl,blob=true
     -display gtk,gl=on
     -boot d
     -serial stdio