Finish CUDA 12.9 migration and use branch-25.06 workflows (#117)

This PR reverts shared-workflows branches to `branch-25.06` and ensures builds use CUDA 12.8.

CUDA 12.9 will be used in the test matrix but not for builds in RAPIDS 25.06. See rapidsai/build-planning#173 (comment) for more information.

Authors:
  - Bradley Dice (https://github.com/bdice)
  - Gil Forsyth (https://github.com/gforsyth)

Approvers:
  - Don Acosta (https://github.com/acostadon)

URL: #117

Author: bdice

docs/cugraph-docs/source/installation/getting_cugraph.md

@@ -40,7 +40,7 @@ Replace the package name in the example below to the one you want to install.
 Install and update cuGraph using the conda command:
 
 ```bash
-conda install -c rapidsai -c conda-forge -c nvidia cugraph cuda-version=12.9
+conda install -c rapidsai -c conda-forge -c nvidia cugraph cuda-version=12.8
 ```
 
 Alternatively, use `cuda-version=11.8` for packages supporting CUDA 11.

docs/cugraph-docs/source/installation/source_build.md

@@ -42,7 +42,7 @@ files](https://github.com/rapidsai/cugraph/blob/main/conda/environments).
 conda env create --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_cuda-118_arch-x86_64.yaml
 
 # for CUDA 12.x
-conda env create --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_cuda-129_arch-x86_64.yaml
+conda env create --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_cuda-128_arch-x86_64.yaml
 
 
 # activate the environment
@@ -60,7 +60,7 @@ conda env update --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_
 conda activate cugraph_dev
 
 # for CUDA 12.x
-conda env update --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_cuda-129_arch-x86_64.yaml
+conda env update --name cugraph_dev --file $CUGRAPH_HOME/conda/environments/all_cuda-128_arch-x86_64.yaml
 conda activate cugraph_dev