This PR fixes the following error for Style/ParallelAssignment when a lambda with parallel assignment is used on the RHS.

$ echo 'a, b = x, -> { a, b = x, y}' | \
RUBOCOP_TARGET_RUBY_VERSION=3.0 bundle exec rubocop --stdin example.rb --only Style/ParallelAssignment -a -d
(snip)

An error occurred while Style/ParallelAssignment cop was inspecting
/Users/koic/src/github.com/rubocop/rubocop/example.rb:1:15.
Parser::Source::TreeRewriter detected clobbering

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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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• 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.