Update Qemu in order to keep building with modern gcc-12
Building Qemu 6.1.0 with gcc-12 fails:
In function 'pte_get_page_mask',
inlined from 'amdvi_page_walk' at ../hw/i386/amd_iommu.c:941:25,
inlined from 'amdvi_do_translate' at ../hw/i386/amd_iommu.c:985:5,
inlined from 'amdvi_translate' at ../hw/i386/amd_iommu.c:1034:5:
../hw/i386/amd_iommu.c:876:38: error: 'oldlevel' may be used uninitialized [-Werror=maybe-uninitialized]
876 | return ~((1UL << ((oldlevel * 9) + 3)) - 1);
| ~~~~~~~~~~~~~~~~^~~~
../hw/i386/amd_iommu.c: In function 'amdvi_translate':
../hw/i386/amd_iommu.c:899:41: note: 'oldlevel' was declared here
899 | unsigned level, present, pte_perms, oldlevel;
| ^~~~~~~~
However Debian testing now defaults to gcc-12 and Qemu v7.0.0 includes a fix.