Bump default CONDA_STORE_SERVER_VERSION

[gabalafou]

Set it to the last version in which the server-vendored version of the UI was still working (i.e., 2023.3.1 at localhost:8080/conda-store).

Does not fix, but it is tangentially related to:

• https://github.com/conda-incubator/conda-store-ui/issues/408.