Fix cross-platform flakiness in ERC root-resolution test

test_root_resolves_to_project_schematic built its project directly in tmp_path,
where the autouse _set_test_search_paths fixture also drops a
test_project.kicad_pro. With two .kicad_pro files in one directory, root
resolution returned whichever os.listdir yielded first — myproject on ext4,
test_project on APFS — so it passed on Linux and failed on macOS. Anchor the
test's project in its own subdirectory so the walk stops at the intended root.

tests/test_schematic_analysis.py

@@ -2,6 +2,7 @@
 
 import pytest
 
+
 @pytest.mark.unit
 class TestRunSchematicErc:
     """Tests for the run_schematic_erc tool."""
@@ -182,14 +183,22 @@ class TestErcJsonParsing:
 
         from mckicad.tools.schematic_analysis import run_schematic_erc
 
-        # Create a project structure with root + sub-sheet
+        # Anchor the project in its own subdirectory. The autouse
-        pro_file = tmp_path / "myproject.kicad_pro"
+        # _set_test_search_paths fixture drops a second "test_project.kicad_pro"
+        # into tmp_path; keeping our project one level down means the root walk
+        # finds *this* project's .kicad_pro and stops before it reaches (and is
+        # confused by) the sibling. Without this, resolution depends on
+        # os.listdir order, which differs between ext4 and APFS.
+        proj_dir = tmp_path / "myproject"
+        proj_dir.mkdir()
+
+        pro_file = proj_dir / "myproject.kicad_pro"
         pro_file.write_text("{}")
 
-        root_sch = tmp_path / "myproject.kicad_sch"
+        root_sch = proj_dir / "myproject.kicad_sch"
         root_sch.write_text('(kicad_sch (version 20231120) (uuid "root"))\n')
 
-        sub_dir = tmp_path / "sub"
+        sub_dir = proj_dir / "sub"
         sub_dir.mkdir()
         sub_sch = sub_dir / "power.kicad_sch"
         sub_sch.write_text('(kicad_sch (version 20231120) (uuid "sub"))\n')