Azure kubelogin (CLI)

What's Changed

• Add kubelogin-version.txt as a release asset to avoid GitHub API rate limits by @Copilot in https://github.com/Azure/kubelogin/pull/749

Maintenance

• Bump kubelogin build toolchain pins to Go 1.26.3 for CVE-2026-27137 remediation by @Copilot in https://github.com/Azure/kubelogin/pull/753
• Update README with official Azure kubelogin sources by @bcho in https://github.com/Azure/kubelogin/pull/751

Full Changelog: https://github.com/Azure/kubelogin/compare/v0.2.17...v0.2.18