[Fix #6822] Fix Lint/LiteralInInterpolation autocorrection for single quotes

[hoshinotsuyoshi]

Fixes #6822

Current behavior:

Doing $ rubocop --only Lint/LiteralInInterpolation;

source:

x = "ABC".gsub(/(A)(B)(C)/, "D#{'\2'}F")
"foo#{'\n'}bar"
"this is #{'"'} silly"

corrected to:

x = "ABC".gsub(/(A)(B)(C)/, "D\2F")
"foo\nbar"
"this is " silly"

New behavior:

corrected to:

x = "ABC".gsub(/(A)(B)(C)/, "D\\2F")
"foo\\nbar"
"this is \" silly"

---

• 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.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[hoshinotsuyoshi]

force-pushed 69151d4 (using String#gsub) to 5849678 (using String#inspect) 🙏

---

I want to fix another pattern bug,

"this is #{'"'} silly"

corrected to (at latest rubocop);

"this is " silly"

new behavior, 5849678 correctly works;

"this is \" silly"

[bbatsov]

Thanks!