Fix false positive for Lint/LiteralAssignmentInCondition

[koic]

This PR fixes the following false positive for Lint/LiteralAssignmentInCondition when using parallel assignment with splat operator:

return if do_something do |z|
  x, y = *z
end

$ bundle exec rubocop example.rb --only Lint/LiteralAssignmentInCondition
Inspecting 1 file
W

Offenses:

example.rb:2:8: W: Lint/LiteralAssignmentInCondition: Don't use literal assignment = *z
in conditional, should be == or non-literal operand.
  x, y = *z
       ^^^^

1 file inspected, 1 offense detected

This is a false positive because ruby -w doesn't warn.

---

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• Added tests.
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