Adds the coverralls completion action

The coverralls completion action tells coverralls when to send the
information about the coverrage back to github

.github/workflows/build.yml

@@ -54,6 +54,18 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}"
           COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}
+  coveralls:
+    name: Indicate completion to coveralls.io
+    needs: integration-test
+    runs-on: ubuntu-latest
+    container: python:3-slim
+    steps:
+    - name: Finished
+      run: |
+        pip3 install --upgrade coveralls
+        coveralls --service=github --finish
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
   # make sure the python side of things works on windows
   other-os-tests:
     name: Test ${{ matrix.os }} Python ${{ matrix.python-version }}