sameSite cookie issues with stats.wp.com/w.js

### Steps to reproduce the behavior
In this particular case, I:
1. Started a JN site and view the Jetpack dashboard.
2. View the console.

#### What I expected to happen
No errors

#### What actually happened

### Context
a8c tracks call in stats.wp.com/w.js which is the origin of these cookies.

#### Browser / OS version
Firefox Dev (92b9), macOS 11.5.1

#### Is this specific to the applied theme? Which one?
n/a

#### Does this happen on simple or atomic sites or both?
Probably both; should be happening with anything loading w.js.

#### Is there any console output or error text?
Yes:
```
Cookie “tk_tc” will be soon rejected because it has the “SameSite” attribute set to “None” or an invalid value, without the “secure” attribute. To know more about the “SameSite“ attribute, read https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cookie/SameSite
```

#### Level of impact (Does it block purchases? Does it affect more than just one site?)
Medium. It'll likely lead to failure to track soon.

#### Reproducibility (Consistent, Intermittent) Leave empty for consistent.

#### Screenshot / Video: If applicable, add screenshots to help explain your problem.

Start by reproducing the warning in Firefox Dev while viewing the Jetpack dashboard, then inspect the cookie setup in stats.wp.com/w.js, identified as the origin of tk_tc. Done means the SameSite warning no longer appears and tracking continues to work; the issue does not name a repository file or test.

Written by the indexing model from the issue text.