Correct a `InternalAffairs/NodeFirstOrLastArgument`

[ydah]

❯ bundle exec rubocop -A Inspecting 40 files .................C......................

Offenses:

lib/rubocop/cop/capybara/specific_finders.rb:79:30: C: [Corrected] InternalAffairs/NodeFirstOrLastArgument: Use #first_argument instead of #arguments[0]. range_between(node.arguments[0].source_range.end_pos, ^^^^^^^^^^^^

40 files inspected, 1 offense detected, 1 offense corrected

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Before submitting the PR make sure the following are checked:

• [x] Feature branch is up-to-date with main (if not - rebase it).
• [x] Squashed related commits together.
• [ ] Added tests.
• [ ] Updated documentation.
• [ ] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• [x] The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• [ ] Added the new cop to config/default.yml.
• [ ] The cop is configured as Enabled: pending in config/default.yml.
• [ ] The cop documents examples of good and bad code.
• [ ] The tests assert both that bad code is reported and that good code is not reported.
• [ ] Set VersionAdded: "<<next>>" in default/config.yml.

If you have modified an existing cop's configuration options:

• [ ] Set VersionChanged: "<<next>>" in config/default.yml.

[pirj]

Thank you!