examples/suit_update/test: use 'suit seq_no' to get version

[fjmolinas]

Contribution description

Follow-up to #17941, it changes the examples/suit_update teste to use the suit seq_no command and adapts that command formatting to be as riotboot hdr dump.

Testing procedure

• murdock should test the shell changes
• exmples/suit_update rebase on nanocoap: follow-up fixes #17950

Issues/PRs references

Depends on #17950 since the current SUIT CoAP is broken.

[fjmolinas]

re-ran the test for good measure

suit_coap: started.
Starting the shell
>
>
> ifconfig
current-slot
Running from slot 0
> ifconfig
Iface  4  HWaddr: AA:04:26:28:76:39
          L2-PDU:1500  MTU:1500  HL:64  RTR
          Source address length: 6
          Link type: wired
          inet6 addr: fe80::a804:26ff:fe28:7639  scope: link  VAL
pinging node...
PING fe80::a804:26ff:fe28:7639%riot0(fe80::a804:26ff:fe28:7639%riot0) 56 data bytes

--- fe80::a804:26ff:fe28:7639%riot0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 41.698/41.698/41.698/0.000 ms
pinging node succeeded.
TEST PASSED