Add missing cfg annotation

Author: LaurenzV

scripts/gen-shaping-tests.py

@@ -204,9 +204,12 @@ def convert_test_folder(root_dir, hb_shape_exe, tests_dir, tests_name, custom):
 def convert_test_files(root_dir, hb_shape_exe, tests_dir, tests_name, files, custom):
     fonts = set()
 
+    macos_snippet = "#[cfg(target_os = \"macos\")]\n" if tests_name == "macos" else ""
+    
     rust_code = (
         "// WARNING: this file was generated by ../scripts/gen-shaping-tests.py\n"
-        "\n"
+        "\n" +
+        macos_snippet +
         "use crate::shape;\n"
         "\n"
     )