"...email address" in the "Buy Mozilla Privacy Pack" banner could be changed to plural

[Bianca-O]

Build:
Stage

Affected platforms:
Windows 10 64-bit
macOS 10.14
Android 11
iOS 14.6

Browsers tested on:
Firefox

Preconditions:
The user hasn't upgraded to MPP.

Steps to reproduce:

1. Navigate to https://stage.fxprivaterelay.nonprod.cloudops.mozgcp.net and log in using an existing account.
2. Observe the "Buy Mozilla Privacy Pack" banner text.

Actual result:
Email address is at singular.

Expected result:
Email address is at plural.

[AOiegas]

Verified this issue on stage, both on Windows 10 and Android 9. The error was corrected and it's looking good now.