Bug#1022184: grub2: Update compiler version (currently: gcc-10)

[Bastian Germann]

Source: grub2
Version: 2.06-4

This package build-depends on gcc-11; on amd64, this package can
be built with gcc-11.  If the package cannot be built on any
architecture with gcc-11 because of a compiler bug, please file a
report for gcc-12. Else, please update the compiler version.

You might even be able to update to the current standard gcc-12.
However, this requires changing the package; a test build failed
with dangling-pointer errors.