Fix a false positive for Layout/TrailingEmptyLines

[koic]

This PR fixes a false positive for Layout/TrailingEmptyLines to prevent the following incorrect autocorrection when inspecting the % form string %\n\n.

First, Layout/TrailingEmptyLines cop detects an offense upon inspection, but it's valid syntax:

$ echo "x = %\n\n" | be rubocop --stdin example.rb --only Layout/TrailingEmptyLines
Inspecting 1 file
C

Offenses:

example.rb:2:1: C: [Correctable] Layout/TrailingEmptyLines: 2 trailing blank lines detected.

1 file inspected, 1 offense detected, 1 offense autocorrectable

Next, Layout/TrailingEmptyLines cop autocorrects to an invalid syntax and Lint/Syntax occurs:

$ echo "x = %\n\n" | be rubocop --stdin example.rb --only Layout/TrailingEmptyLines -a
Inspecting 1 file
F

Offenses:

example.rb:1:5: F: Lint/Syntax: unterminated string meets end of file
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter, under AllCops)
x = %
^
example.rb:2:1: C: [Corrected] Layout/TrailingEmptyLines: 2 trailing blank lines detected.

1 file inspected, 2 offenses detected, 1 offense corrected
====================
x = %

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Before submitting the PR make sure the following are checked:

• 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.