cli/command/plugins: runRemove: fix incorrect use of errors.Join

[thaJeztah]

• follow-up to / fixes cli/command/plugins: use errors.Join instead of custom cli.Errors, and deprecate cli.Errors #5547 (comment)

commit 71ebbb8 replaced the use of the custom "cli.Errors" type for stdlib's errors.Join, however it made a mistake by calling errors.Join for each error occurred, which "nests" each error instead of putting each error at the same level.

Thanks to Paweł Gronowski for spotting this on the pull request

- Description for the changelog

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.42%. Comparing base (4808d1b) to head (37b25f2).
Report is 12 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5779   +/-   ##
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  Coverage   59.42%   59.42%           
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  Files         347      347           
  Lines       29398    29400    +2     
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+ Hits        17469    17471    +2     
  Misses      10957    10957           
  Partials      972      972