qemu: only run with kvm when intended

Author: astro

lib/runners/qemu.nix

@@ -63,7 +63,7 @@ let
 
   accel =
     if microvmConfig.cpu == null
-    then "accel=kvm:tcg"
+    then "accel=kvm"
     else "accel=tcg";
 
   # PCI required by vfio-pci for PCI passthrough