test: the archive check's own git gets a plain Windows path (P11c)

local.rs's archive_git handed git the canonical \\?\ path the product's
git already no longer sees. Same helper (root::plain_path). The other
Command::new("git") tests are Unix-only files (backups.rs, format_upgrade,
open_while_held) or use paths from tempfile, not canonicalize.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-mcp/src/local.rs

@@ -3171,7 +3171,11 @@ mod tests {
     /// git, on the books' own archive: what it said.
     fn archive_git(dir: &Path, args: &[&str]) -> String {
         let out = std::process::Command::new("git")
-            .arg(format!("--git-dir={}", dir.join("archive.git").display()))
+            .arg(format!(
+                "--git-dir={}",
+                // A canonical path on Windows carries `\\?\`, which git refuses.
+                ledger_store::root::plain_path(&dir.join("archive.git")).display()
+            ))
             .args(args)
             .output()
             .unwrap();