Update miniconda install in tests

Mambaforge has been deprecated, since all functionality moved into
Miniforge.

Author: dwhswenson

.github/workflows/tests.yml

@@ -24,10 +24,10 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
-      - uses: conda-incubator/setup-miniconda@v2
+      - uses: conda-incubator/setup-miniconda@v3
         with:
           python-version: ${{ matrix.CONDA_PY }}
-          miniforge-variant: Mambaforge
+          miniforge-version: latest
       - name: "Install"
         run: |
           curl -OLk https://raw.githubusercontent.com/openpathsampling/openpathsampling/master/devtools/conda_ops_dev_install.sh