Drop mambaforge as it is deprecated

Author: jacobtomlinson

.github/workflows/ci-build.yaml

@@ -28,7 +28,6 @@ jobs:
       - name: Setup Conda Environment
         uses: conda-incubator/setup-miniconda@v3.3.0
         with:
-          miniforge-variant: Mambaforge
           miniforge-version: latest
           environment-file: binder/environment.yml
           activate-environment: dask-examples

.github/workflows/ci-update-dependencies.yaml

@@ -28,7 +28,6 @@ jobs:
       - name: Setup Conda Environment
         uses: conda-incubator/setup-miniconda@v3.3.0
         with:
-          miniforge-variant: Mambaforge
           miniforge-version: latest
           environment-file: binder/environment-base.yml
           auto-activate-base: false