[Bug]: Incorrect link when trying to buy Jetpack Security for multisite page

### Quick summary

In WP admin of the multisite page, when I click on `Jetpack > Dashboard > Plans` I'm redirected to https://jetpack.com/redirect/?source=jetpack-plans&site=www.mailpoet.com.

When I click on the `Get Security` button to purchase `Security` plan, an error message is shown on the checkout:

The message is correct, but the link leads to
`https://jetpack.com/support/backup/#does-jetpack-backup-support-multisite`
when it should lead to
`https://jetpack.com/support/scan/#does-jetpack-scan-support-multisite`
because Backup supports multisite, but Scan does not.

I think [this is the code](https://github.com/Automattic/wp-calypso/blob/73084528ba5552fce1e0792442ea9372d49c872c/client/my-sites/checkout/cart/cart-messages.tsx#L111) with the wrong link.

### Steps to reproduce

1. Install Jetpack on multisite page
2. Click on `Jetpack > Dashboard > Plans` (in the top menu)
3. You are redirected to https://cloud.jetpack.com/pricing
4. Select **Security** plan
5. Observe error message

### What you expected to happen

The `More info` links to https://jetpack.com/support/scan/#does-jetpack-scan-support-multisite

### What actually happened

The `More info` links to https://jetpack.com/support/backup/#does-jetpack-backup-support-multisite

### Context

Wanted to install Jetpack scan on mailpoet.com

### Browser

_No response_

### Simple/Atomic

_No response_

### Other notes

_No response_

### Reproducibility

Consistent

### Severity

Some (< 50%)

### Available workarounds?

No but the platform is still usable

### Workaround details

_No response_

Start in client/my-sites/checkout/cart/cart-messages.tsx around line 111, where the incorrect More info link is identified. Reproduce the multisite Jetpack Security checkout flow and verify that the link points to the Scan support URL rather than the Backup support URL.

Written by the indexing model from the issue text.