ci: build git 2.28 via alpine
Created by: ggilmore
see https://buildkite.com/sourcegraph/sourcegraph/builds/71240#fd44ba3e-9040-4f3a-a3db-cb4752977c49 for an example build
Created by: ggilmore
see https://buildkite.com/sourcegraph/sourcegraph/builds/71240#fd44ba3e-9040-4f3a-a3db-cb4752977c49 for an example build