Update dotnetcore.yml

Author: romantitov

.github/workflows/dotnetcore.yml

@@ -35,3 +35,11 @@ jobs:
       with:
           name: code-coverage
           path: TestResults
+          
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v4
+      with:
+          files: TestResults/**/*.opencover.xml
+          flags: unittests
+          fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}