Set repository mtime to GitHub `updated_at` time

CGit reads the repository modification time from the following
locations, in order from top to bottom:

1. agefile
2. repo.git/refs/heads/{default_branch | "master"}
3. repo.git/packed-refs

(https://git.zx2c4.com/cgit/tree/ui-repolist.c?id=bd6f5683f6cde4212364354b3139c1d521f40f39#n35)

Update the `/refs/heads/{default_branch}` file mtime when cloning and
updating the repo to match the GitHub `updated_at` time.

This ensures that when mirroring old repositories, they don't appear at
the top of the CGit repository index list when sorting by age.

1 files changed, 2 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 854cc11..18ec2a4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,6 +5,8 @@ edition = "2018"
 
 [dependencies]
 anyhow = "1.0.40"
+chrono = "0.4.19"
+filetime = "0.2.14"
 git2 = "0.13.20"
 reqwest = { version = "0.11.3", features = ["json"] }
 serde = { version = "1.0.126", features = ["derive"] }