Ensure the add_new and add_new_item labels are the same

[dkotter]

Description of the Change

In testing on WP 6.7, the Add New button for the Safe Redirect Manager post type is showing as Safe Redirect Manager instead of Create Redirect Rule. This causes an E2E failure and also doesn't make much sense, since this button shows right next to the title which is also Safe Redirect Manager.

Seems WP 6.7 changed something around the add_new and add_new_item labels so this PR ensures our post type uses the same text for both.

Before on WP 6.7:

After on WP 6.7 (and older):

How to test the Change

1. Go to the Safe Redirect Manager page under Tools
2. Ensure the button shown at the top says Create Redirect Rule
3. Test on both WP 6.7 and 6.6

Changelog Entry

Fixed - Ensure the add new button shows proper text

Credits

Props @dkotter, @jeffpaul

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[jeffpaul]

Looks good, waiting on e2e tests to pass before merging