Fix false positives for Rails/CompactBlank

[koic]

This PR fixes false positives for Rails/CompactBlank when using collection.reject!.

reject!(&:blank?) is not equivalent to compact_blank!:

{}.reject!(&:blank?)            # => nil
{}.reject! { |_k, v| v.blank? } # => nil
{}.compact_blank!               # => {}

This PR prioritizes safer behavior with plain hashes and arrays.

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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).
• Feature branch is up-to-date with master (if not - rebase it).
• 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.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.