rpc: fix a flaky test of the websocket (#33002)

Found in
https://github.com/ethereum/go-ethereum/actions/runs/17803828253/job/50611300621?pr=32585

```
--- FAIL: TestClientCancelWebsocket (0.33s)
panic: read tcp 127.0.0.1:36048->127.0.0.1:38643: read: connection reset by peer [recovered, repanicked]

goroutine 15 [running]:
testing.tRunner.func1.2({0x98dd20, 0xc0005b0100})
	/opt/actions-runner/_work/_tool/go/1.25.1/x64/src/testing/testing.go:1872 +0x237
testing.tRunner.func1()
	/opt/actions-runner/_work/_tool/go/1.25.1/x64/src/testing/testing.go:1875 +0x35b
panic({0x98dd20?, 0xc0005b0100?})
	/opt/actions-runner/_work/_tool/go/1.25.1/x64/src/runtime/panic.go:783 +0x132
github.com/ethereum/go-ethereum/rpc.httpTestClient(0xc0001dc1c0?, {0x9d5e40, 0x2}, 0xc0002bc1c0)
	/opt/actions-runner/_work/go-ethereum/go-ethereum/rpc/client_test.go:932 +0x2b1
github.com/ethereum/go-ethereum/rpc.testClientCancel({0x9d5e40, 0x2}, 0xc0001dc1c0)
	/opt/actions-runner/_work/go-ethereum/go-ethereum/rpc/client_test.go:356 +0x15f
github.com/ethereum/go-ethereum/rpc.TestClientCancelWebsocket(0xc0001dc1c0?)
	/opt/actions-runner/_work/go-ethereum/go-ethereum/rpc/client_test.go:319 +0x25
testing.tRunner(0xc0001dc1c0, 0xa07370)
	/opt/actions-runner/_work/_tool/go/1.25.1/x64/src/testing/testing.go:1934 +0xea
created by testing.(*T).Run in goroutine 1
	/opt/actions-runner/_work/_tool/go/1.25.1/x64/src/testing/testing.go:1997 +0x465
FAIL	github.com/ethereum/go-ethereum/rpc	0.371s
```

In `testClientCancel` we wrap the server listener in `flakeyListener`,
which schedules an unconditional close of every accepted connection
after a random delay, if the random delay is zero then the timer fires
immediately, and then the http client paniced of connection reset by
peer.

Here we add a minimum 10ms to ensure the timeout won't fire immediately.

Signed-off-by: jsvisa <[email protected]>

Author: jsvisa

rpc/client_test.go

@@ -973,7 +973,7 @@ func (l *flakeyListener) Accept() (net.Conn, error) {
 
 	c, err := l.Listener.Accept()
 	if err == nil {
-		timeout := time.Duration(rand.Int63n(int64(l.maxKillTimeout)))
+		timeout := max(time.Millisecond*10, time.Duration(rand.Int63n(int64(l.maxKillTimeout))))
 		time.AfterFunc(timeout, func() {
 			log.Debug(fmt.Sprintf("killing conn %v after %v", c.LocalAddr(), timeout))
 			c.Close()