Add workflow to test PyPI yank capability via org secret

Author: nikhilwoodruff

.github/workflows/test_pypi_yank.yml

@@ -0,0 +1,19 @@
+name: Test PyPI yank capability
+
+on:
+  workflow_dispatch:
+
+jobs:
+  test-yank:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install twine
+        run: pip install twine
+
+      - name: Attempt to yank policyengine-uk 0.35.0
+        env:
+          TWINE_USERNAME: __token__
+          TWINE_PASSWORD: ${{ secrets.PYPI }}
+        run: |
+          pip install twine
+          twine yank policyengine-uk 0.35.0 --reason "Test: verifying org secret has yank permissions" || echo "YANK FAILED (exit $?)"