sysutils/nerdctl: Update to 2.1.6

Changelog:

• https://github.com/containerd/nerdctl/releases/tag/v2.1.4
• https://github.com/containerd/nerdctl/releases/tag/v2.1.5
• https://github.com/containerd/nerdctl/releases/tag/v2.1.6

PR: 290650
Reported by: Laurent Chardon <laurent.chardon@gmail.com> (maintainer)