Moderate: libheif security update (Amazon Linux 2023)

Package updates are available for Amazon Linux 2023 that fix the following vulnerabilities: CVE-2025-68431: libheif is an HEIF and AVIF file format decoder and encoder. Prior to version 1.21.0, a crafted HEIF that exercises the overlay image item path triggers a heap buffer over-read in `HeifPixelImage::overlay()`. The function computes a negative row length (likely from an unclipped overlay rectangle or invalid offsets), which then underflows when converted to `size_t` and is passed to `memcpy`, causing a very large read past the end of the source plane and a crash. Version 1.21.0 contains a patch. As a workaround, avoid decoding images using `iovl` overlay boxes.