Only build oldest and newest Python variants for nightly builds

[jdblischak]

In an effort to reduce both the CI and storage required for the nightly feedstock builds, I updated the tiledb-py-feedstock to only build the oldest and newest Python versions supported by conda-forge, currently 3.8 and 3.12, respectively.

I confirmed this works locally as well as in a manual run, which showed the CI files for 3.9, 3.10, and 3.11 being deleted.

Note that this will require the occasional manual maintenance as the conda-forge global pin for Python/numpy are updated. This PR is based on https://github.com/conda-forge/conda-forge-pinning-feedstock/blob/5ccbd396dc675580aff241f5b313e4b00a2ad9d6/recipe/conda_build_config.yaml#L764

[jdblischak]

Follow up to confirm that this worked as expected last night. The Python variants were added to conda_build_config.yaml in TileDB-Inc/tiledb-py-feedstock@a18a80e, therefore conda-smithy removed the 3.9, 3.10, and 3.11 build variants in TileDB-Inc/tiledb-py-feedstock@c71eee0, which resulted in a build matrix of only 10 total jobs. Note that the builds only failed because on Monday night we check for deprecated API usage (#133)