Release linux version 6.6.13-1+apertis2

• Inject -Wno-error=format-overflow -Wno-error=format-truncation: In contrary to Debian, we use by default -Wformat-overflow=2 -Wformat-truncation=2 in Apertis, but kernel is built with -Werror which makes the kernel FTBFS with: "cc1: all warnings being treated as errors". In order to avoid this error, we don't treat these warnings as errors.

• Drop dependency on image to headers package: This dependency was added in https://salsa.debian.org/kernel-team/linux/-/merge_requests/903 to avoid users using headers of a different version then the associated image. Unfortunately, this change has a side effect in Apertis because it is no longer possible to build a sysroot without pulling a kernel image which is not needed. Since the upstream change has no benefit for Apertis and leads to issue to generate sysroot, we revert it by dropping the dependency.