[MAIN] Fix CI conda runner (#598)

* use setup miniconda action

.github/workflows/CI.yml

@@ -310,6 +310,7 @@ jobs:
       matrix:
         # OS [ubuntu-latest, macos-latest, windows-latest]
         os: [ubuntu-latest]
+        python-version: [3.9]
 
       # do not cancel all in-progress jobs if any matrix job fails
       fail-fast: false
@@ -324,32 +325,36 @@ jobs:
 
           key: ${{ runner.os }}-pip-${{hashFiles('requirements/environment-tests.yml') }}-${{ hashFiles('**/CI.yml') }}-${{ steps.date.outputs.date }}
 
-      - name: Add conda to system path
-        run: |
-          # $CONDA is an environment variable pointing to the root of the miniconda directory
-          echo $CONDA/bin >> $GITHUB_PATH
+      - uses: conda-incubator/setup-miniconda@3b0f2504dd76ef23b6d31f291f4913fb60ab5ff3 # corresponds to v2.2.0
+        with:
+          auto-update-conda: true
+          python-version: ${{ matrix.python-version }}
+          activate-environment: elephant
+          environment-file: requirements/environment-tests.yml
+          auto-activate-base: false
+          use-only-tar-bz2: true # IMPORTANT: This needs to be set for caching to work properly!
+
       - name: Install dependencies
+        shell: bash -l {0}
         run: |
-          conda config --add channels conda-forge # bugfix with scipy==1.8.1: libstdcxx-ng 12.1.0 required
-          conda update conda
-          conda install -c conda-forge libstdcxx-ng=12 # fix libstdc++.so.6: version for new scipy versions > 1.9.1
-          conda env update --file requirements/environment-tests.yml --name base
-          activate base
-          conda install -c conda-forge openmpi
-          pip install -r requirements/requirements-tests.txt
-          pip install pytest
-          pip install pytest-cov coveralls
-          pip install .
+          python --version
+          conda env list
+          conda install mpi4py openmpi
+          conda install pytest
+          conda install pytest-cov coveralls
+          pip install -e .
+
       - name: List packages
+        shell: bash -l {0}
         run: |
-          activate base
           pip list
           conda list
           python --version
+
       - name: Test with pytest
+        shell: bash -l {0}
         run: |
-          activate base
-          pytest --cov=elephant --import-mode=importlib
+          pytest --cov=elephant
 
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