When you watch a repository, you get notifications for any new pull requests and issues that are created, including those not mentioning you.
Tip: You will automatically watch any repositories you create or that are created by your team in an organization.
On GitHub, navigate to the main page of the repository.
In the upper-right corner, in the "Watch" list, select Watching.
Disabling automatic watching
In the upper-right corner of any page, click your profile photo, then click Settings.
In the user settings sidebar, click Notifications.
Under "How you receive notifications," uncheck Automatically watch repositories.