windows: reduce Linux VM memory

windows: reduce Linux VM memory

There have been a lot of Windows job failures lately due to
qemu errors caused by insufficient Jenkins slave memory:

  ERROR    internal error: process exited while connecting to
  monitor: 2024-04-21T11:37:28.922183Z qemu-system-x86_64: cannot
  set up guest memory 'pc.ram': Cannot allocate memory

Each Windows job spins up two virtual machines: a Linux one with
64GB of ram and a Windows VM with 8GB of ram. Since the Windows job
no longer uses memstore, we can probably reduce the Linux vm memory
to 16GB.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>