fix(icmp_echo): fix incorrect test expectation logic

examples/protocols/icmp_echo/pytest_icmp_echo.py

@@ -83,6 +83,8 @@ def test_protocols_icmp_echo_ipv6_only(dut: Dut) -> None:
     logging.info(f'Connected AP with IPv6={ipv6}')
     interface_nr = dut.expect(r'Connected on interface: [a-z]{2}\d \((\d+)\)', timeout=30)[1].decode()
 
+    dut.expect_exact('esp>')
+
     # ping our own address to simplify things
     dut.write('ping -I {} {} -c 5'.format(interface_nr, ipv6))