Any search you do in the main search field (preceded with "This repository") when you are in a GitHub repo page will return:
- result in code
- and issues
Note: The shortcut / will focus on the search field and search within the context of a repository.
Note: that shortcut doesn't work with a french keyboard on Firefox. And it only works if I type ':' (again on a French Keyboard) in Chrome. So your mileage may vary. With US locale, this should work fine.
Note that in 2022 (9 years later), there is a command palette, and you can customize the keyboard shortcuts.