I have a Gmail account for Android ROM testing purpose. And I kept receiving this annoying email from Google anytime I use that account to sign in Gmail (most of the time it's a clean flashed Android phone which I will wipe out later). Here is how to disable the email notification.

Login to Gmail using the account which you wish to stop receiving notifications. At the very bottom right of Inbox page, you will see this:

Last account activity: 0 minutes ago
Details

Click on "Details", then at the bottom of the pop up window:

Alert preference: Show an alert for unusual activity. change

Click "change" and then choose "Never show an alert for unusual activity". Then "Apply", then "Disable alerts".

Thanks to:

https://webapps.stackexchange.com/questions/85727/make-google-stop-sending-new-sign-in-from-emails/86432#86432?s=77a2ae5697034627aab8f8eb0388f4ce