If folks want to continue searching open source, https://sourcegraph.com/search does not require sign in and also includes major projects that are not on GitHub.
(Full disclosure: I'm the Sourcegraph CTO)
(Full disclosure: I'm the Sourcegraph CTO)
I remember longing for the ability for github's search to rival git clone + grep, but I never expected a login wall to come with it. IIRC I expected the login wall to just be because the feature was in beta and would be removed when it became the primary search.