update submodule and patches to QEMU 8.1.5

update submodule and patches to QEMU 8.1.5

Most notable fixes from a Proxmox VE perspective are:

* "virtio-net: correctly copy vnet header when flushing TX"
  To prevent a stack overflow that could lead to leaking parts of the
  QEMU process's memory.
* "hw/pflash: implement update buffer for block writes"
  To prevent an edge case for half-completed writes. This potentially
  affected EFI disks.
* Fixes to i386 emulation and ARM emulation.

No changes for patches were necessary (all are just automatic context
changes).

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>