Fix an error for Lint/NumberConversion

[koic]

This PR fixes the following error for Lint/NumberConversion when using multiple number conversion methods:

$ cat example.rb
case foo.to_f
when 0.0
bar
else
baz
end.to_i

$ bundle exec rubocop --only Lint/NumberConversion -A -d
(snip)

An error occurred while Lint/NumberConversion cop was inspecting /Users/koic/src/github.com/koic/rubocop-issues/number_conversion/example.rb:1:5.
Parser::Source::TreeRewriter detected clobbering
/Users/koic/.rbenv/versions/3.2.1/lib/ruby/gems/3.2.0/gems/parser-3.2.2.3/lib/parser/source/tree_rewriter.rb:427:in `trigger_policy'

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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.

[bbatsov]

The conversion looks a big ugly for multi-line forms, but the fix is good overall. Thanks!