Remove request isinstance Exception checks from switch

[TheJulianJES]

This removes two dead isinstance check in the switch platform. Zigpy cannot return an exception as the result here. It'll always raise instead.

Another PR will remove all Status.SUCCESS checks for the result. We'll have to be slightly more careful with that change because ZCL errors like UNSUPP_CLUSTER_COMMAND don't raise(?) But they should also never occur, really.

Related discussion in:

• Fix stuck light transitioning flag after task cancellation #672 (comment)

[TheJulianJES]

Unlike #678, it is safe to just remove these two isinstance checks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.51%. Comparing base (1b6b19f) to head (d729016).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #677   +/-   ##
=======================================
  Coverage   97.51%   97.51%           
=======================================
  Files          62       62           
  Lines       10941    10941           
=======================================
  Hits        10669    10669           
  Misses        272      272           

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