crypto/tls: "use of closed network connection" in TestDialTimeout

[bcmills]

Seen on the linux-amd64-longtest builder (https://build.golang.org/log/9fbd6f6c2639b72e2d147e1d16d45784fdc2e069):

--- FAIL: TestDialTimeout (0.01s)
    tls_test.go:183: accept tcp 127.0.0.1:38709: use of closed network connection
FAIL
FAIL	crypto/tls	0.702s

CC @FiloSottile

[bcmills]

No recurrences since 2019. Possibly fixed by some intervening change?

greplogs --dashboard -md -l -e '(?ms)FAIL: TestDialTimeout.*FAIL\s+crypto/tls' --since=2019-01-01

2019-08-26T16:36:15-a80c5f0/linux-amd64-longtest