validation: Confirm yaml file contents are an object (instructlab#1084)

The top-level element of a yaml document can be an object (key-value
pairs) or a list. We now test and provide an error message if the
top-level element is not an object.

See instructlab/instructlab#1170

Signed-off-by: BJ Hargrave <[email protected]>

.github/scripts/check-yaml.py

@@ -10,7 +10,7 @@
 from functools import cache, partial
 from importlib.resources.abc import Traversable
 from pathlib import Path
-from typing import List, Optional, Union
+from typing import List, Mapping, Optional, Union
 
 # Third Party
 import yaml
@@ -155,6 +155,12 @@ def check(self) -> int:
                 if not parsed:
                     self.error(file=taxonomy_path, message="The file is empty")
                     continue
+                if not isinstance(parsed, Mapping):
+                    self.error(
+                        file=taxonomy_path,
+                        message="The file is not valid. The top-level element is not an object with key-value pairs.",
+                    )
+                    continue
 
                 version = parsed.get("version", 1)
                 if not isinstance(version, int):