test flake: data race: coderd/devtunnel: TestTunnel

[johnstcn]

Seen here: https://github.com/coder/coder/actions/runs/6407370722/job/17394013311?pr=10043

==================
WARNING: DATA RACE
Write at 0x00c000055450 by goroutine 18:
  runtime.closechan()
      /opt/hostedtoolcache/go/1.20.8/x64/src/runtime/chan.go:357 +0x0
  golang.zx2c4.com/wireguard/tun/netstack.(*netTun).Close()
      /home/runner/go/pkg/mod/golang.zx2c4.com/wireguard@v0.0.0-20230704135630-469159ecf7d1/tun/netstack/tun.go:178 +0xde
  golang.zx2c4.com/wireguard/device.(*Device).Close()
      /home/runner/go/pkg/mod/golang.zx2c4.com/wireguard@v0.0.0-20230704135630-469159ecf7d1/device/device.go:381 +0x1e8
  github.com/coder/wgtunnel/tunneld.(*API).Close()
      /home/runner/go/pkg/mod/github.com/coder/wgtunnel@v0.1.12/tunneld/tunneld.go:136 +0x64
  github.com/coder/coder/v2/coderd/devtunnel_test.newTunnelServer.func2()
      /home/runner/actions-runner/_work/coder/coder/coderd/devtunnel/tunnel_test.go:222 +0x30
  testing.(*common).Cleanup.func1()
      /opt/hostedtoolcache/go/1.20.8/x64/src/testing/testing.go:1150 +0x193
  testing.(*common).runCleanup()
      /opt/hostedtoolcache/go/1.20.8/x64/src/testing/testing.go:1328 +0x1e9
  testing.tRunner.func2()
      /opt/hostedtoolcache/go/1.20.8/x64/src/testing/testing.go:1570 +0x52
  runtime.deferreturn()
      /opt/hostedtoolcache/go/1.20.8/x64/src/runtime/panic.go:476 +0x32
  testing.(*T).Run.func1()
      /opt/hostedtoolcache/go/1.20.8/x64/src/testing/testing.go:1629 +0x47

Full output: https://gist.github.com/johnstcn/b91175c5dad874c17444911add364b40