net: TestLookupGoogleSRV data race flake

[mvdan]

https://build.golang.org/log/da10353ff948b8ee551f28949ba441271588db28

==================
WARNING: DATA RACE
Read at 0x00c420487580 by goroutine 9:
  net.TestClosingListener.func1()
      /tmp/workdir/go/src/net/listen_test.go:711 +0x44

Previous write at 0x00c420487580 by goroutine 79:
  net.TestClosingListener()
      /tmp/workdir/go/src/net/listen_test.go:726 +0x254
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169

Goroutine 9 (running) created at:
  net.TestClosingListener()
      /tmp/workdir/go/src/net/listen_test.go:709 +0x1ac
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169

Goroutine 79 (finished) created at:
  testing.(*T).Run()
      /tmp/workdir/go/src/testing/testing.go:812 +0x535
  testing.runTests.func1()
      /tmp/workdir/go/src/testing/testing.go:1036 +0xa4
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169
  testing.runTests()
      /tmp/workdir/go/src/testing/testing.go:1034 +0x4bf
  testing.(*M).Run()
      /tmp/workdir/go/src/testing/testing.go:954 +0x271
  net.TestMain()
      /tmp/workdir/go/src/net/main_test.go:50 +0x46
  main.main()
      b074/_testmain.go:526 +0x224
==================
==================
WARNING: DATA RACE
Read at 0x00c420192180 by goroutine 9:
  net.(*TCPListener).Accept()
      /tmp/workdir/go/src/net/tcpsock_posix.go:133 +0x2f6
  net.TestClosingListener.func1()
      /tmp/workdir/go/src/net/listen_test.go:711 +0x5a

Previous write at 0x00c420192180 by goroutine 79:
  net.listenTCP()
      /tmp/workdir/go/src/net/tcpsock_posix.go:160 +0x102
  net.ListenTCP()
      /tmp/workdir/go/src/net/tcpsock.go:319 +0xe0
  net.Listen()
      /tmp/workdir/go/src/net/dial.go:592 +0x6f6
  net.TestClosingListener()
      /tmp/workdir/go/src/net/listen_test.go:726 +0x21e
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169

Goroutine 9 (running) created at:
  net.TestClosingListener()
      /tmp/workdir/go/src/net/listen_test.go:709 +0x1ac
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169

Goroutine 79 (finished) created at:
  testing.(*T).Run()
      /tmp/workdir/go/src/testing/testing.go:812 +0x535
  testing.runTests.func1()
      /tmp/workdir/go/src/testing/testing.go:1036 +0xa4
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:769 +0x169
  testing.runTests()
      /tmp/workdir/go/src/testing/testing.go:1034 +0x4bf
  testing.(*M).Run()
      /tmp/workdir/go/src/testing/testing.go:954 +0x271
  net.TestMain()
      /tmp/workdir/go/src/net/main_test.go:50 +0x46
  main.main()
      b074/_testmain.go:526 +0x224
==================
--- FAIL: TestLookupGoogleSRV (0.03s)
	testing.go:722: race detected during execution of test
FAIL
FAIL	net	8.503s

[gopherbot]

Change https://golang.org/cl/70230 mentions this issue: net: fix data race in TestClosingListener