Split cuda versions for notebook testing

[raydouglass]

Description

Follow up to #14648

Since rapidsai/docker tests the notebooks on both CUDA 11.8 & 12.0, we need a CUDA 11.8 version of the test_notebooks file key.

Without this change rdfg wlll always generate an environment with cuda-version=12.0 even when the matrix is for CUDA 11.8 and then it will conflict with other repos (as see here).

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[raydouglass]

Environment before:

$ rapids-dependency-file-generator --file_key test_notebooks --matrix "cuda=11.8;arch=$(arch);py=3.10" --output conda
# This file is generated by `rapids-dependency-file-generator`.
# To make changes, edit dependencies.yaml and run `rapids-dependency-file-generator`.
channels:
- rapidsai
- rapidsai-nightly
- dask/label/dev
- pytorch
- conda-forge
- nvidia
dependencies:
- cuda-version=12.0
- ipython
- notebook
- python=3.10
- scipy
name: test_notebooks_cuda-118_arch-x86_64_py-310

After this change:

$ rapids-dependency-file-generator --file_key test_notebooks --matrix "cuda=11.8;arch=$(arch);py=3.10" --output conda
# This file is generated by `rapids-dependency-file-generator`.
# To make changes, edit dependencies.yaml and run `rapids-dependency-file-generator`.
channels:
- rapidsai
- rapidsai-nightly
- dask/label/dev
- pytorch
- conda-forge
- nvidia
dependencies:
- cuda-version=11.8
- ipython
- notebook
- python=3.10
- scipy
name: test_notebooks_cuda-118_arch-x86_64_py-310

[raydouglass]

/merge

[bdice]

I updated this branch to include #14723, which should unblock tests.