Avoid redundant selector lookup in Capybara/SpecificActions

[ydah]

Avoid the redundant selector lookup in Capybara/SpecificActions.

on_send already normalizes the find argument with last_selector(arg) before calling specific_action. This changes specific_action to use that normalized selector directly when looking up SPECIFIC_ACTION, keeping the behavior the same while making the control flow easier to follow.

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with main (if not - rebase it).
• Squashed related commits together.
• [-] Added tests.
• [-] Updated documentation.
• [-] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• 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.
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If you have modified an existing cop's configuration options:

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