tests: childhurd: Prefer “-cpu max” over “-cpu host”.

“-cpu host” can sometimes, for unclear reasons, lead to this error from
QEMU 8.1.1:

  qemu-system-x86_64: CPU model 'host' requires KVM or HVF

This commit fixes it.

Inspired by
<47b56e7c19>.

* gnu/tests/virtualization.scm (run-childhurd-test)[test]: Prefer
“-cpu max” over “-cpu host”.

Change-Id: I11a8a68bb0532fe1f3fd2c34b4a7a5fdb7bccb57

gnu/tests/virtualization.scm

@@ -298,10 +298,10 @@ (define test
                        (ice-9 match))
 
           (define marionette
-            ;; Emulate the host CPU so that KVM is available inside as well
-            ;; ("nested KVM"), provided
+            ;; Emulate as much as the host CPU supports so that, possibly, KVM
+            ;; is available inside as well ("nested KVM"), provided
             ;; /sys/module/kvm_intel/parameters/nested (or similar) allows it.
-            (make-marionette (list #$vm "-cpu" "host")))
+            (make-marionette (list #$vm "-cpu" "max")))
 
           (test-runner-current (system-test-runner #$output))
           (test-begin "childhurd")