test: fix Windows-only file_hash directory-rejection assertion

`File::open` on a directory fails outright on Windows (different OS error
kind), whereas on Unix it opens and the is_file() guard rejects it with
InvalidInput. The production code rejects directories on both platforms;
only pin the specific InvalidInput kind off-Windows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: mikolalysenko

crates/socket-patch-core/src/patch/file_hash.rs

@@ -109,6 +109,13 @@ mod tests {
 
         let result = compute_file_git_sha256(dir.path()).await;
         let err = result.expect_err("hashing a directory must error");
+
+        // On Unix a directory opens successfully and the `is_file` guard
+        // rejects it with `InvalidInput`. On Windows `File::open` on a
+        // directory fails at the open call itself (a different OS error kind),
+        // so we only pin the specific kind off-Windows. Either way the
+        // contract that matters holds: it errors and never hashes.
+        #[cfg(not(windows))]
         assert_eq!(err.kind(), std::io::ErrorKind::InvalidInput);
 
         // It must specifically NOT have returned the empty-blob hash.