fix git tests (#1747)

the git tests were failing on my local machine due to gpg signing config
in my ~/.gitconfig. tests should not be affected by ~/.gitconfig, so
configure them to ignore it.

codex-rs/core/src/git_info.rs

@@ -111,9 +111,14 @@ mod tests {
     // Helper function to create a test git repository
     async fn create_test_git_repo(temp_dir: &TempDir) -> PathBuf {
         let repo_path = temp_dir.path().to_path_buf();
+        let envs = vec![
+            ("GIT_CONFIG_GLOBAL", "/dev/null"),
+            ("GIT_CONFIG_NOSYSTEM", "1"),
+        ];
 
         // Initialize git repo
         Command::new("git")
+            .envs(envs.clone())
             .args(["init"])
             .current_dir(&repo_path)
             .output()
@@ -122,6 +127,7 @@ mod tests {
 
         // Configure git user (required for commits)
         Command::new("git")
+            .envs(envs.clone())
             .args(["config", "user.name", "Test User"])
             .current_dir(&repo_path)
             .output()
@@ -129,6 +135,7 @@ mod tests {
             .expect("Failed to set git user name");
 
         Command::new("git")
+            .envs(envs.clone())
             .args(["config", "user.email", "test@example.com"])
             .current_dir(&repo_path)
             .output()
@@ -140,6 +147,7 @@ mod tests {
         fs::write(&test_file, "test content").expect("Failed to write test file");
 
         Command::new("git")
+            .envs(envs.clone())
             .args(["add", "."])
             .current_dir(&repo_path)
             .output()
@@ -147,6 +155,7 @@ mod tests {
             .expect("Failed to add files");
 
         Command::new("git")
+            .envs(envs.clone())
             .args(["commit", "-m", "Initial commit"])
             .current_dir(&repo_path)
             .output()