fix: check action['action'] instance type before parsing action cls

[ChengyangDu]

Check action['action'] instance type to avoid undesired llm outputs, which may cause runtime type error.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (main@ae2b857). Click here to learn what that means.

Files	Patch %	Lines
opendevin/events/action/__init__.py	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1599   +/-   ##
=======================================
  Coverage        ?   62.49%           
=======================================
  Files           ?       91           
  Lines           ?     3738           
  Branches        ?        0           
=======================================
  Hits            ?     2336           
  Misses          ?     1402           
  Partials        ?        0           

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[enyst]

Thanks!