wgengine: use slices.Clone in two places

Updates #cleanup

Change-Id: I1cb30efb6d09180e82b807d6146f37897ef99307
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f