Fix a false positive for Rails/Pluck

[koic]

This PR fixes a false positive for Rails/Pluck
when using block argument in [] to prevent the following incompatible autocorrect.

-x.collect { |a| a[foo...a.to_someghing] }
+x.pluck(foo...a.to_someghing)

The a is not defined in the autocorrected code.

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