Set "Github Actions" shell on "Windows".

Author: KelSolaar

.github/workflows/continuous-integration.yml

@@ -121,6 +121,7 @@ jobs:
 #        echo ::set-env name=CI_SLACK_SUCCESS_NOTIFICATION::%CI_SLACK_SUCCESS_NOTIFICATION%
 #        echo ::set-env name=CI_SLACK_FAILURE_NOTIFICATION::%CI_SLACK_FAILURE_NOTIFICATION%
 #        echo ::set-env name=COVERALLS_REPO_TOKEN::%COVERALLS_REPO_TOKEN%
+#      shell: cmd
 #    - name: Set up Python ${{ matrix.python-version }}
 #      uses: actions/setup-python@v1
 #      with:
@@ -131,28 +132,34 @@ jobs:
 #        python get-poetry.py --preview
 #        set PATH=%USERPROFILE%\.poetry\bin;%PATH%
 #        echo ::set-env name=PATH::%PATH%
+#      shell: cmd
 #    - name: Install Package Dependencies
 #      run: |
 #        call poetry install
 #        FOR /F %%a IN ('poetry env info -p') DO SET CI_VIRTUAL_ENVIRONMENT=%%a
 #        echo ::set-env name=CI_VIRTUAL_ENVIRONMENT::%CI_VIRTUAL_ENVIRONMENT%
 #        call %CI_VIRTUAL_ENVIRONMENT%\scripts\activate
 #        python -c "import imageio;imageio.plugins.freeimage.download()"
+#      shell: cmd
 #    - name: Lint with flake8
 #      run: |
 #        call %CI_VIRTUAL_ENVIRONMENT%\scripts\activate
 #        flake8 %CI_PACKAGE% --count --show-source --statistics
+#      shell: cmd
 #    - name: Test with nosetests
 #      run: |
 #        call %CI_VIRTUAL_ENVIRONMENT%\scripts\activate
 #        python -W ignore -m nose -v --nocapture --with-doctest --doctest-options=+ELLIPSIS --with-coverage --cover-package=%CI_PACKAGE% %CI_PACKAGE%
+#      shell: cmd
 #    - name: Upload Coverage to coveralls.io
 #      if: matrix.python-version == '3.6' || matrix.python-version == '3.7'
 #      run: |
 #        call %CI_VIRTUAL_ENVIRONMENT%\scripts\activate
 #        IF "%COVERALLS_REPO_TOKEN%"=="" (echo "COVERALLS_REPO_TOKEN" secret is undefined!) ELSE (coveralls)
+#      shell: cmd
 #    - name: Notify Slack
 #      if: always()
 #      run: |
 #        IF "${{ job.status }}"=="Success" (set CI_SLACK_NOTIFICATION=%CI_SLACK_SUCCESS_NOTIFICATION%) ELSE (set CI_SLACK_NOTIFICATION=%CI_SLACK_FAILURE_NOTIFICATION%)
 #        IF "%CI_SLACK_WEBHOOK%"=="" (echo "SLACK_WEBHOOK" secret is undefined!) ELSE (curl -k -d %CI_SLACK_NOTIFICATION% -X POST %CI_SLACK_WEBHOOK%)
+#      shell: cmd