Update unit tests workflow to use Ubuntu 20.04 and setup Python 3.9

.github/workflows/unittests.yml

@@ -4,25 +4,16 @@ on: push
 
 jobs:
   test:
-    runs-on: ubuntu-latest
-    defaults:
-      run:
-        shell: bash -l {0}
+    runs-on: ubuntu-20.04
 
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
 
-      - uses: conda-incubator/setup-miniconda@v3
+      - uses: actions/setup-[email protected]
         with:
-          auto-update-conda: true
           python-version: 3.9
-          activate-environment: test
-
-      # - uses: actions/[email protected]
-      #   with:
-      #     python-version: 3.9
 
       - name: Install dependencies
         run: |