Use git config --global user.email for email address in automatic Co-authored-by (#32624)

Release Notes:

- Automatic population of `Co-authored-by` now uses `git config --global
user.email`

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Conrad <conrad@zed.dev>

crates/collab/src/db/tests/buffer_tests.rs

@@ -126,12 +126,16 @@ async fn test_channel_buffers(db: &Arc<Database>) {
                 peer_id: Some(rpc::proto::PeerId { id: 1, owner_id }),
                 replica_id: 0,
                 is_host: false,
+                committer_name: None,
+                committer_email: None,
             },
             rpc::proto::Collaborator {
                 user_id: b_id.to_proto(),
                 peer_id: Some(rpc::proto::PeerId { id: 2, owner_id }),
                 replica_id: 1,
                 is_host: false,
+                committer_name: None,
+                committer_email: None,
             }
         ]
     );