Add codecov token

Author: bkoelman

.github/workflows/build.yml

@@ -138,6 +138,8 @@ jobs:
         dotnet test --no-build --configuration Release --collect:"XPlat Code Coverage" --logger "GitHubActions;summary.includeSkippedTests=true"
     - name: Upload coverage to codecov.io
       if: matrix.os == 'ubuntu-latest'
+      env:
+        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       uses: codecov/codecov-action@v4
       with:
         fail_ci_if_error: true