Erroneous quotes in tmp_path_retention_policy example in docs

[RFCArrow]

pytest: 8.3.2
OS: Ubuntu 22.04

doc/en/reference/reference.rst contains the following example for tmp_path_retention_policy

.. confval:: tmp_path_retention_policy



   Controls which directories created by the `tmp_path` fixture are kept around,
   based on test outcome.

    * `all`: retains directories for all tests, regardless of the outcome.
    * `failed`: retains directories only for tests with outcome `error` or `failed`.
    * `none`: directories are always removed after each test ends, regardless of the outcome.

   .. code-block:: ini

        [pytest]
        tmp_path_retention_policy = "all"

However, if the example value tmp_path_retention_policy = "all" is used in pytest.ini then the following error is encountered:

INTERNALERROR> ValueError: tmp_path_retention_policy must be either all, failed, none. Current input: "all".

This error is avoided if the value is not wrapped in quotes: tmp_path_retention_policy = all

I believe the docs should be updated to remove the erroneous quotes in the example.