CI: disable secure boot in mkosi GHA runs

Booting a guest with secure boot is broken in Azure due to a hypervisor
bug. Disable it for now. Given there's no option, need to edit
the configuration on the fly.

.github/workflows/mkosi.yml

@@ -117,6 +117,8 @@ jobs:
 
     - name: Configure
       run: |
+        # XXX: drop after the HyperV bug that breaks secure boot KVM guests is solved
+        sed -i "s/'firmware'\s*:\s*'auto'/'firmware' : 'uefi'/g" test/*/meson.build
         tee mkosi.local.conf <<EOF
         [Distribution]
         Distribution=${{ matrix.distro }}