wgengine/router: demote TestDebugListRules fail to skip

Updates #3360

Change-Id: Ic5c98ea03f3171c13ab9293a0ae74d17fd04d149
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f