Error details are captured in the Error::Git variant; the raw git
output on stderr is redundant and noisy in test output.

Assisted-by: GLM-5.1 via pi

diff --git a/src/quire.rs b/src/quire.rs
index ff21c87..d12c304 100644
--- a/src/quire.rs
+++ b/src/quire.rs
@@ -161,6 +161,7 @@ impl Repo {
             .env("GIT_CONFIG_KEY_0", "http.extraHeader")
             .env("GIT_CONFIG_VALUE_0", github_auth_header(token))
             .stdout(std::process::Stdio::null())
+            .stderr(std::process::Stdio::null())
             .status()
             .map_err(crate::Error::Io)?;