Notification: "Stats are booming" notification doesn't work when site URL contains a subdirectory

[rachelmcr]

When WordPress is installed on a subdirectory, the link to the site's stats in the "stats are booming" notification doesn't work.

Steps to reproduce

1. Start with a site with WordPress in a subdirectory.
2. Install and activate the Jetpack plugin.
3. Connect Jetpack to a WordPress.com account.
4. Trigger the "stats are booming" notification or just visit this link that's used in the notification: https://wordpress.com/stats/day/SITE_BASE_URL?startDate=2020-07-06 where SITE_BASE_URL is the site URL without the subdirectory.
5. Notice that you are taken to the All Sites stats view instead of the correct stats view for your site, at this URL: https://wordpress.com/stats/day?site=SITE_BASE_URL
6. Visit the link again, but add the site's subdirectory like this: https://wordpress.com/stats/day/SITE_BASE_URL::SUBDIRECTORY?startDate=2020-07-06 (note the :: between the base URL and the subdirectory). Notice the correct stats view now loads.

What I expected

I expected the notification to contain a link to the site's stats with the specified date highlighted.

What happened instead

The link doesn't contain the full site URL (including the subdirectory) so it redirects to the All Sites stats view instead.

Browser / OS version

Chrome 83.0.4103.116 / macOS 10.15.5

Screenshot / Video

Example site URL: https://magenta-cod.jurassic.ninja/subdir/
Correct stats link: https://wordpress.com/stats/day/magenta-cod.jurassic.ninja::subdir?startDate=2020-07-06
Link as formatted in the notification: https://wordpress.com/stats/day/magenta-cod.jurassic.ninja?startDate=2020-07-06

Actual stats view	Expected stats view

Context / Source

Reported by @sararosso in Slack (internal ref: p1594072063135700-slack-automattic) and reproduced on a test site.

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