go: net/http: TestServerShutdown failures

#!watchflakes
post <- pkg == "net/http" && test == "TestServerShutdown" && `server should be shut down`

Issue created automatically to collect these failures.

Example (log):

2022/10/25 00:24:18 http2: server: error reading preface from client 127.0.0.1:58560: bogus greeting "CONNECT golang.fake.tld:"
2022/10/25 00:24:18 http2: server: error reading preface from client 127.0.0.1:59626: bogus greeting "CONNECT golang.fake.tld:"
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:57220: read tcp 127.0.0.1:43019->127.0.0.1:57220: i/o timeout
--- FAIL: TestServerShutdown (0.00s)
    --- FAIL: TestServerShutdown/h2 (0.06s)
        serve_test.go:5564: second request should fail. server should be shut down
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:37530: EOF
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:42388: EOF
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:55964: write tcp 127.0.0.1:39597->127.0.0.1:55964: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:55944: write tcp 127.0.0.1:39597->127.0.0.1:55944: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:47390: write tcp 127.0.0.1:43357->127.0.0.1:47390: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:55990: write tcp 127.0.0.1:39597->127.0.0.1:55990: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:47416: write tcp 127.0.0.1:43357->127.0.0.1:47416: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:47396: write tcp 127.0.0.1:43357->127.0.0.1:47396: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:55978: write tcp 127.0.0.1:39597->127.0.0.1:55978: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:47432: write tcp 127.0.0.1:43357->127.0.0.1:47432: use of closed network connection
2022/10/25 00:24:18 http: TLS handshake error from 127.0.0.1:47440: write tcp 127.0.0.1:43357->127.0.0.1:47440: use of closed network connection

— watchflakes