fix typo in serialize_file doc-string

[LVivona]

What does this PR do?

function serialize_file within binding/python/src/lib.rs contains a doc-string typo

Now

/// Serializes raw data into file.
///
/// Args:
///     tensor_dict (`Dict[str, Dict[Any]]`):
///         The tensor dict is like:
///             {"tensor_name": {"dtype": "F32", "shape": [2, 3], "data": b"\0\0"}}
///     filename (`str`, or `os.PathLike`):
///         The name of the file to write into.
///     metadata (`Dict[str, str]`, *optional*):
///         The optional purely text annotations
///
/// Returns:
///     (`NoneType`):
///         On success return None

Previous

/// Serializes raw data.
///
/// Args:
///     tensor_dict (`Dict[str, Dict[Any]]`):
///         The tensor dict is like:
///             {"tensor_name": {"dtype": "F32", "shape": [2, 3], "data": b"\0\0"}}
///     filename (`str`, or `os.PathLike`):
///         The name of the file to write into.
///     metadata (`Dict[str, str]`, *optional*):
///         The optional purely text annotations
///
/// Returns:
///     (`bytes`):
///         The serialized content.

[daskol]

Could you fix tensor_dict example too. It uses string "F32" dtype while prepare() routine actually infers dtype from fully-qualified string "float32".