The Surface Go 3 is a tablet with a detachable Type Cover keyboard,
but its firmware reports SMBIOS chassis type 9 (Laptop), so hostnamed
reports "laptop". Override it to "convertible", which is what hostnamed
already uses for SMBIOS chassis type 0x20 (Detachable).
Tested on a Surface Go 3 with the DMI modalias
dmi:bvnMicrosoftCorporation:...:svnMicrosoftCorporation:pnSurfaceGo3:...
