[#2593] Fix missing coverage data in codecov

Previously our coverage data was imporperly being shipped to codecov on
two accounts:

1. We were not combining the data files from each run of the test matrix
   (elastic and main)
2. The main test run was not running with the appropriate --concurrency
   flag and thus it was missing out on coverage data due to not taking
   into account all test processes.

This commit addresses both issues and ensures codecov receives the
full coverage data file (both runs, all parallel processes).

.github/workflows/ci.yml

@@ -63,24 +63,51 @@ jobs:
       - name: Run tests
         run: |
           if [ "${{ matrix.test-type }}" = "main" ]; then
-            coverage run \
+            coverage run -p --concurrency=multiprocessing \
               src/manage.py test src \
               --parallel \
               --exclude-tag=e2e \
               --exclude-tag=elastic
           elif [ "${{ matrix.test-type }}" = "elastic" ]; then
-            coverage run src/manage.py test src --tag=elastic --exclude-tag=e2e
+            coverage run -p src/manage.py test src --tag=elastic --exclude-tag=e2e
           else
             echo "Error: Unknown test type '${{ matrix.test-type }}'"
             exit 1
           fi
-
         env:
           DJANGO_SETTINGS_MODULE: open_inwoner.conf.ci
           SECRET_KEY: dummy
           DB_USER: postgres
           DB_PASSWORD: ''
-
+      - name: Persist coverage data files
+        uses: actions/upload-artifact@v4
+        with:
+          name: ${{ matrix.test-type }}
+          path: .coverage*
+
+  upload_coverage:
+    needs: tests
+    name: Upload coverage information to codecov
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Git repository
+        uses: actions/checkout@v2
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      - name: Install coverage.py
+        # We only need coverage, but we need to match the version that was used
+        # to generate the coverage files. Grab it from the dependencies.
+        run: grep "^coverage" requirements/ci.txt | xargs -r pip install
+      - uses: actions/download-artifact@v4
+        with:
+          path: coverages
+      - name: Combine the coverage files
+        run: |
+          mv coverages/main/.coverage* .
+          mv coverages/elastic/.coverage* .
+          coverage combine
       - name: Publish coverage report
         uses: codecov/codecov-action@v3
         with: