3.10.1

CHANGES:

• Add the NixOS CI to test ocaml-git (@Et7f3, #600, #473)
• Specify few more headers fields when we fetch/push via HTTP (@reynir, @hannesm, @dinosaure, #603, #601)
• Improve the error message about Smart_git.Endpoint.of_string (@reynir, @dinosaure, #605, #604)