F-Strings not fully supported

[det]

Documentation states that:

enable_f_strings: bool
Are f"{expression}" strings supported? Disabled in all dialects by default.

This is not accurate. Only identifiers are supported, not expressions.

Example error:

    2: error: Not a valid identifier: `config.description`
         --> path/to/file.star:17:26
          |
       17 |         description = f"{config.description} ({num_files} files)"
          |                          ^^^^^^^^^^^^^^^^^^
          |