Fix IPv6 address case in server_list function

[Anvil]

Description

When specifying an IPv6 address in faust.App as broker, faust passes to aiokafka an incorrectly-transformed value.

e.g:

When I write this:

faust.App('mob', broker=f'kafka://[1234:5678::9abc]')

yarl.URL constructor receives the strings as is, but the returned object .host attribute is 1234:5678::9abc. So, the server_list function in transport/drivers/aiokafka.py creates 1234:5678::9abc:9092, which, while not syntactically incorrect, is a different IPv6 address. Also, the port information is lost in the process.

I've checked the yarl module and there does not seem to be any attribute/method to retrieve the enclosed IPv6 address. This small change intend to fix this behavior, on faust side.

L156 is assumed as a "is it an IPv6 address" check. While it could be better, I found it's good enough for me. :)

[codecov-io]

Codecov Report

Merging #66 (400f686) into master (e239534) will decrease coverage by 0.02%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
- Coverage   64.03%   64.00%   -0.03%     
==========================================
  Files          99       99              
  Lines       10290    10296       +6     
  Branches     1157     1159       +2     
==========================================
+ Hits         6589     6590       +1     
- Misses       3547     3552       +5     
  Partials      154      154              

Impacted Files	Coverage Δ
faust/transport/drivers/aiokafka.py	33.33% <14.28%> (-0.18%)	⬇️

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[max-k]

@patkivikram could you approve this ?
Anvil is one of my teammates and we did this together.
Thank you very much.