Backup & Scan: Menu should link to Calypso Green

Originally part of https://github.com/Automattic/wp-calypso/issues/50225.

As reported in p1HpG7-bcl-p2#comment-44716, the Backups & Scan menu should link to Calypso Green instead of Calypso Blue.

### Context

To quote @folletto the aim of the changes is...

> [i]n short: any flow that starts in WP Admin should end in WP Admin, any flow that starts in Calypso should end in Calypso. If no other way it’s possible, the switch should be explicit.

(see: p1HpG7-bcl-p2#comment-44627).

#### Guiding principles

- From Calypso Blue (.com), a link to WP Admin that:
- has a .com equivalent, should be changed to that.
- has only a WP Admin equivalent, should have an explicit label (maybe even with the external link icon), so the user knows it’s going outside.
- From WP Admin, a link to .com that:
- has a WP Admin or Calypso Green equivalent, should be changed to that.
- has only a .com page, should still link to that, but find a label that says so explicitly (maybe even with the external link icon), so the user knows it’s going outside.

The issue identifies the Backups & Scan menu and the Calypso Blue and Calypso Green destinations, but does not name a file or test. Locate the menu entry, verify where it currently links, and confirm that it points to Calypso Green when finished.

Written by the indexing model from the issue text.