AO3-5937 "Save" button visible on bookmarks when logged out and on a tag's bookmarks page

[forceofcalm]

Pull Request Checklist

• Have you read "How to write the perfect pull request"?
• Have you read the contributing guidelines?
• Have you added tests for any changed functionality?
• Have you added the Jira issue number
  as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
• Do you have fewer than 5 pull requests already open? If not, please wait
  until they are reviewed and merged before creating new pull requests.

Issue

https://otwarchive.atlassian.net/browse/AO3-5937

Purpose

Wraps the "save" and "saved" actions for bookmarks in a logged_in? check.

Testing Instructions

I have left a comment for clarification on the JIRA ticket.

Credit

calm (they/them)

[ceithir]

Could you add an integration test covering this fix?

[brianjaustin]

I think these should help with the ERB lint warning (I have not had a chance to test locally though, so some further nudges may be required)

[forceofcalm]

I'm writing the integration test for this now (or at least, trying to), and I've noticed that the Save button is actually an <li> element styled like a button. For accessibility reasons, this should be an actual <button> element. A change like that is out of the scope of this ticket, but should be noted somewhere.