Downgrade 'codecov-action' version from v4 to v3 (#6930)

The 'codecov-action@v4' requires an organization-level upload token, not
a single repo upload token, so we're temporarily downgrading it until we
can generate an organization-level upload token.

Reference: codecov/codecov-action#1273

.github/workflows/ci.yml

@@ -76,7 +76,7 @@ jobs:
           docker cp tests:/app/coverage.xml ./coverage.xml
           docker cp tests:/app/junit.xml /tmp/test-results/unit-tests/results.xml
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v3
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
       - name: Store Test Results