1.38.0 pre-release is ready for testing

I would like signal to downstream that with this version, cargo uses libgit2-sys crate which broke the compatibility with libgit2-0.28 branch and depend on unreleased libgit2 version.

Running cargo break at runtime with such error:

$ cargo install test
    Updating crates.io index
error: failed to fetch `https://github.com/rust-lang/crates.io-index`

Caused by:
  invalid version 3 on git_proxy_options; class=Invalid (3)

FreeBSD already have a local patch to restore the compatibility at lang/rust-nightly/files/patch-vendor_libgit2-sys_lib.rs , and I intent to use it too for OpenBSD too.