ci: adding python matrix for conda

Author: lachlangrose

.github/workflows/conda.yml

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest",  "windows-latest","macos-latest"]
-        python-version: ["3.7"]
+        python-version: ["3.7,3.8,3.9"]
     steps:
       - uses: conda-incubator/setup-miniconda@v2
         with: