`kraken`: search broken by change to `Client._pairs: dict[str, Pair]`

[goodboy]

Perdon perdon 😂

likely caused by #477 ..

Traceback (most recent call last):
  File "/home/goodboy/repos/tractor/tractor/_runtime.py", line 196, in _invoke
    res = await coro
  File "/home/goodboy/repos/piker/piker/brokers/kraken/feed.py", line 457, in open_symbol_search
    {item[0]['altname']: item[0]
  File "/home/goodboy/repos/piker/piker/brokers/kraken/feed.py", line 457, in <dictcomp>
    {item[0]['altname']: item[0]
TypeError: 'Pair' object is not subscriptable

[2] > /home/goodboy/repos/piker/piker/brokers/kraken/feed.py(457)<dictcomp>()
-> {item[0]['altname']: item[0]

[goodboy]

Pretty sure fixed in #484