Loosen callback future type

[ahuang11]

Fixes #6118.

I print the type of future and it results in <class 'asyncio.futures.Future'>

I also do:

            print(isinstance(future, asyncio.Future), isinstance(future, asyncio.futures.Future))

which returns True, True

but I still get:

ValueError: ClassSelector parameter 'ChatInterface._callback_future' value must be an instance of Future, not <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /Users/ahuang/miniconda3/envs/panel/lib/python3.10/asyncio/futures.py:385]>.

So I just set to param.Parameter and it works.

Also, I needed to specify the height manually in the app, or else no messages show up:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7f25eb1) 84.67% compared to head (33cf9bf) 84.63%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6120      +/-   ##
==========================================
- Coverage   84.67%   84.63%   -0.04%     
==========================================
  Files         296      296              
  Lines       44100    44096       -4     
==========================================
- Hits        37341    37321      -20     
- Misses       6759     6775      +16     

Flag	Coverage Δ
ui-tests	40.68% <0.00%> (-0.01%)	⬇️
unitexamples-tests	72.63% <100.00%> (-0.05%)	⬇️

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