SNOW-1065172-gh-workflow-optimization: upload coverage to codecov

Sometimes on GCP this test stalls. Until we figure out what is the real prblem we will retry and add timeout.

.github/workflows/build_test.yml

@@ -220,3 +220,12 @@ jobs:
         with:
           name: combined_htmlcov
           path: htmlcov
+      - name: Uplaod to codecov
+        uses: codecov/codecov-action@v4
+        with:
+          directory: artifacts/coverage.xml_*/coverage.xml
+          env_vars: OS,PYTHON
+          fail_ci_if_error: true
+          flags: unittests
+          token: ${{ secrets.CODECOV_TOKEN }}
+          verbose: true