fix: update the docstring in table_type property

[roykoand]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates docstrings in google/cloud/bigquery/table.py to include 'SNAPSHOT' and 'MATERIALIZED_VIEW' as valid table types. The review feedback indicates that the list of possible table types is still incomplete, specifically missing 'CLONE', and suggests adding an Oxford comma for improved clarity and consistency in the docstrings.

[gemini-code-assist]

The list of possible table types is incomplete. According to the BigQuery API documentation, 'CLONE' is also a valid value for the table type. Additionally, using an Oxford comma (a comma before the 'or') is generally preferred for clarity in lists of three or more items and improves consistency across the library.

Suggested change

	Possible values are ``'TABLE'``, ``'VIEW'``, ``'MATERIALIZED_VIEW'``,
	``'SNAPSHOT'`` or ``'EXTERNAL'``.
	Possible values are 'TABLE', 'VIEW', 'MATERIALIZED_VIEW',
	'SNAPSHOT', 'CLONE', or 'EXTERNAL'.

[roykoand]

I am not sure what BigQuery API documentation AI reviewer references, but when I run the following snippet for the CLONE type table I get the TABLE type:

>> table = client.get_table("dataset.clone")
>> table.table_type
'TABLE'

while in the INFORMATION_SCHEMA.TABLES it says CLONE in table_type column