Update package publishing workflow

Author: samwelkanda

.github/workflows/publish.yml

@@ -10,15 +10,19 @@ jobs:
     name: Create release and publish distribution to TestPyPI
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - name: Checkout code
+        uses: actions/checkout@v2
       - name: Set up Python 3.8
+        uses: actions/setup-python@v1
         with:
           python-version: 3.8
-      - name: Install dependencies
-        run: >-
-          python -m pip install --upgrade pip
-          python -m pip install flit
-      - name: Publish distibution to TestPyPI
-        if: github.repository == 'microsoftgraph/msgraph-sdk-python-core' && github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
-        run: >-
-          flit publish --repository https://test.pypi.org/legacy/ --username msgraphsdkteam --password ${{ secrets.TEST_PYPI_API_TOKEN }}
+      - name: Install flit
+        run: |
+          pip install flit
+      - name: Publish the distibution to TestPyPI
+        if: github.repository == 'microsoftgraph/msgraph-sdk-python-core'
+        run: flit publish
+        env:
+          FLIT_INDEX_URL: https://test.pypi.org/legacy/
+          FLIT_USERNAME: __token__
+          FLIT_PASSWORD: ${{ secrets.TEST_PYPI_API_TOKEN }}