tests/unit: Replace g_memdup() by g_memdup2()

tests/unit: Replace g_memdup() by g_memdup2()

Per https://discourse.gnome.org/t/port-your-module-from-g-memdup-to-g-memdup2-now/5538

  The old API took the size of the memory to duplicate as a guint,
  whereas most memory functions take memory sizes as a gsize. This
  made it easy to accidentally pass a gsize to g_memdup(). For large
  values, that would lead to a silent truncation of the size from 64
  to 32 bits, and result in a heap area being returned which is
  significantly smaller than what the caller expects. This can likely
  be exploited in various modules to cause a heap buffer overflow.

Replace g_memdup() by the safer g_memdup2() wrapper.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210903174510.751630-24-philmd@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>