Use SettingsErrors when file can't be used as source

Some file formats (at least yaml) allow to represent non dictionnary
values. In such situation we can't add the values read from those files.
Instead of raising a ValueError, we now raise a SettingsError and
indicate we can't parse the related config file.

Author: Julian Vanden Broeck

pydantic_settings/sources.py

@@ -1912,7 +1912,10 @@ def _read_files(self, files: PathType | None) -> dict[str, Any]:
         for file in files:
             file_path = Path(file).expanduser()
             if file_path.is_file():
-                vars.update(self._read_file(file_path))
+                try:
+                    vars.update(self._read_file(file_path))
+                except ValueError as e:
+                    raise SettingsError(f'Parsing error encountered for {file_path}: {e}')
         return vars
 
     @abstractmethod