Open a notification's issue or PR in the default browser.
Command
open {url}
On Linux use xdg-open {url} instead.
Replace {url} with the GitHub HTML URL (e.g., https://github.com/owner/repo/issues/123).
You can also use:
gh issue view {number} --repo {owner}/{repo} --web
gh pr view {number} --repo {owner}/{repo} --web