Add check for secrets and skip steps - stop running ci on new checkin (#22)

Author: hoffmang9

.github/workflows/build.yml

@@ -12,6 +12,11 @@ jobs:
         os: [macos-latest, ubuntu-18.04, windows-latest]
 
     steps:
+    - name: Cancel previous runs on the same branch
+      uses: styfle/[email protected]
+      with:
+        access_token: ${{ github.token }}
+
     - uses: actions/checkout@v1
       with:
         fetch-depth: 0
@@ -22,6 +27,16 @@ jobs:
       with:
         python-version: '3.7'
 
+    - name: Test for secrets access
+      id: check_secrets
+      shell: bash
+      run: |
+        unset HAS_SECRET
+        if [ -n "$SECRET" ]; then HAS_SECRET='true' ; fi
+        echo ::set-output name=HAS_SECRET::${HAS_SECRET}
+      env:
+        SECRET: "${{ secrets.test_pypi_password }}"
+
     - name: Install cibuildwheel
       run: |
         python -m pip install --upgrade pip
@@ -100,6 +115,7 @@ jobs:
       run: pip install twine
 
     - name: Publish distribution to Test PyPI
+      if: steps.check_secrets.outputs.HAS_SECRET
       env:
         TWINE_REPOSITORY_URL: https://test.pypi.org/legacy/
         TWINE_USERNAME: __token__
@@ -108,7 +124,7 @@ jobs:
       run: twine upload --non-interactive --skip-existing --verbose 'dist/*'
 
     - name: Publish distribution to PyPI
-      if: startsWith(github.event.ref, 'refs/tags')
+      if: startsWith(github.event.ref, 'refs/tags') && steps.check_secrets.outputs.HAS_SECRET
       env:
         TWINE_USERNAME: __token__
         TWINE_NON_INTERACTIVE: 1