Ubuntu: USN-8088-1 (CVE-2026-25934): go-git vulnerabilities

go-git is a highly extensible git implementation library written in pure Go. Prior to 5.16.5, a vulnerability was discovered in go-git whereby data integrity values for .pack and .idx files were not properly verified. This resulted in go-git potentially consuming corrupted files, which would likely result in unexpected errors such as object not found. For context, clients fetch packfiles from upstream Git servers. Those files contain a checksum of their contents, so that clients can perform integrity checks before consuming it. The pack indexes (.idx) are generated locally by go-git, or the git cli, when new .pack files are received and processed. The integrity checks for both files were not being verified correctly. This vulnerability is fixed in 5.16.5.