Fix 'qa/specs/features/browser_ui/6_release/deploy_key/add_deploy_key_spec.rb'

What does this MR do?

!22665 (diffs) introduced SHA256 fingerprint for deploy keys but it duplicated a CSS selector in the process.

Unfortunately, the MR was a Community contribution so there was no QA tests run for it.

This removes the duplicated selector and improves the naming a bit.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Closes #196608 (closed).