downgrade codecov/codecov-action action to v3

This reverts commit aa6ae6c.

For some reason, v4 doesn't seem to be available anymore.

Signed-off-by: Manfred Hanke <Manfred.Hanke@tngtech.com>

.github/workflows/build.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Create code coverage report
         run: ./mvnw --batch-mode --no-transfer-progress -e test jacoco:report
       - name: Upload code coverage report
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v3
         with:
           files: target/site/jacoco/jacoco.xml
           name: codecov