Wrap the concurrent futures in an asyncio future

[blink1073]

Follow up to #988

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 72.53%. Comparing base (017c52e) to head (c054752).
Report is 342 commits behind head on main.

Files with missing lines	Patch %	Lines
jupyter_server/services/kernels/handlers.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1001      +/-   ##
==========================================
+ Coverage   72.42%   72.53%   +0.10%     
==========================================
  Files          64       64              
  Lines        8243     8249       +6     
  Branches     1378     1378              
==========================================
+ Hits         5970     5983      +13     
+ Misses       1855     1851       -4     
+ Partials      418      415       -3     

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