Add more awaits for pending kernel in unit tests

[Zsailer]

This is response to jupyter/jupyter_client#732.

jupyter/jupyter_client#732 expands the initial pending kernels work in #593 and makes "shutdown", "interrupt", and "restart" show as pending states.

Jupyter server's unit tests should await these various states when using pending kernels. Here, I've added the needed await statements and made it backwards compatible with old versions of jupyter client (before pending kernels were introduced).

[codecov-commenter]

Codecov Report

Merging #654 (6d97b87) into main (db46446) will increase coverage by 0.02%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##             main     #654      +/-   ##
==========================================
+ Coverage   77.88%   77.91%   +0.02%     
==========================================
  Files         110      110              
  Lines       10405    10418      +13     
  Branches     1400     1401       +1     
==========================================
+ Hits         8104     8117      +13     
  Misses       1911     1911              
  Partials      390      390              

Impacted Files	Coverage Δ
jupyter_server/tests/services/kernels/test_api.py	96.37% <95.00%> (+0.37%)	⬆️

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[blink1073]

Thanks!