Test with and without mamba in conda test

.github/workflows/CI_conda_forge.yml

@@ -21,6 +21,7 @@ jobs:
       matrix:
         python-version: ['3.9']
         os: ['ubuntu-latest', 'macos-latest']
+        use-mamba: [true, false]
     
     steps:
       - uses: actions/checkout@v2
@@ -32,7 +33,12 @@ jobs:
           auto-activate-base: true
           python-version: ${{ matrix.python-version }}
           activate-environment: test
-      - name: "Install pysr-forge"
+          use-mamba: ${{ matrix.use-mamba }}
+      - name: "Install pysr with mamba"
         run: conda activate test && mamba install pysr
+        if: ${{ matrix.use-mamba }}
+      - name: "Install pysr with conda"
+        run: conda activate test && conda install pysr
+        if: ${{ !matrix.use-mamba }}
       - name: "Run tests"
         run: conda activate test && python3 -m unittest test.test && python3 -m unittest test.test_env