Fix an incorrect autocorrect for Style/RedundantException when message is not string

[ydah]

The following autocorrection is performed, but when the message is not a string, the behavior changes after the autocorrection.

# before
raise RuntimeError, Object.new
# => #<RuntimeError: #<Object:0x000000010f369da8>>

# offense
# spec/spec_helper.rb:3:1: C: [Correctable] Style/RedundantException: Redundant RuntimeError argument can be removed.
# raise RuntimeError, Object.new
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

# after
raise Object.new
# => #<TypeError: exception class/object expected>

Therefore, this PR fixes so that the behavior does not change.

irb(main):001:0> e = raise Object.new rescue $!
=> #<TypeError: exception class/object expected>
irb(main):002:0> e = raise RuntimeError, Object.new rescue $!
=> #<RuntimeError: #<Object:0x000000010f369da8>>
irb(main):003:0> e = raise Object.new.to_s rescue $!
=> #<RuntimeError: #<Object:0x000000010f3402a0>>
irb(main):004:0> e = raise RuntimeError.new(Object.new) rescue $!
=> #<RuntimeError: #<Object:0x00000001049d3e88>>
irb(main):005:0> e = raise RuntimeError.new Object.new  rescue $!
=> #<RuntimeError: #<Object:0x00000001079dadc0>>

---

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

I'm guessing you can also mention this case in the cop's documentation examples.

[ydah]

I update this PR. Thank you for review.

[ydah]

Please point out if there is anything in this PR that is still a blocker.

[bbatsov]

It's fine, I just totally forgot about. Sorry about the delay!