OvmfPkg: CI: use ubuntu-22.04 vm_image (Linux only)

OvmfPkg: CI: use ubuntu-22.04 vm_image (Linux only)

Switch over to ubuntu-22.04 as the vm_image for Linux CI jobs.  The
previously used ubuntu-18.04 which is not available anymore since
Dec 1st 2022.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chris Fernald <chfernal@microsoft.com>