mkosi: explicitly disable KVM in GHA runs

mkosi detects whether /dev/kvm is available and uses it if it is. But
some GHA hosts have it, but it's broken and not supported, so we need
to explicitly disable it.

(cherry picked from commit c13e6c720d17a336021a8bd28c5ff5818e61deb6)
(cherry picked from commit b4b04547a73b2d90e33dfa78a2b5c12c05f6e851)
(cherry picked from commit 3b305e40f08104f07a2d2395d698d8e8726df136)

.github/workflows/mkosi.yml

@@ -70,6 +70,10 @@ jobs:
 
         [Output]
         KernelCommandLine=${{ env.KERNEL_CMDLINE }}
+
+        [Host]
+        # Sometimes we run on a host with /dev/kvm, but it is broken, so explicitly disable it
+        QemuKvm=no
         EOF
 
     - name: Build ${{ matrix.distro }}