ci: Add deployment status check workflow (#125)

.github/workflows/pages-status-check.yml

@@ -0,0 +1,14 @@
+name: Check Pages Status
+
+on: page_build
+
+jobs:
+  pages-status-check:
+    runs-on: ubuntu-18.04
+    steps:
+      - name: check status
+        run: |
+          status = '${{ github.event.build.status }}'
+          errormsg = '${{ github.event.build.error.message }}'
+          assert status == 'built', 'Status: {status}\nError: {errormsg}'.format(status, errormsg)
+        shell: python