rpc: fix defer in test (#24490)

Co-authored-by: Felix Lange <fjl@twurst.com>

rpc/server_test.go

@@ -134,14 +134,16 @@ func TestServerShortLivedConn(t *testing.T) {
 		if err != nil {
 			t.Fatal("can't dial:", err)
 		}
-		defer conn.Close()
+
 		conn.SetDeadline(deadline)
 		// Write the request, then half-close the connection so the server stops reading.
 		conn.Write([]byte(request))
 		conn.(*net.TCPConn).CloseWrite()
 		// Now try to get the response.
 		buf := make([]byte, 2000)
 		n, err := conn.Read(buf)
+		conn.Close()
+
 		if err != nil {
 			t.Fatal("read error:", err)
 		}