ci: use staging upload URL for testing

Author: not-matthias

.github/workflows/ci.yml

@@ -93,6 +93,7 @@ jobs:
         if: matrix.codspeed-mode != 'off'
         with:
           mode: ${{ matrix.codspeed-mode }}
+          upload-url: https://api.staging.preview.codspeed.io/upload
           run: examples/google_benchmark_cmake/build/benchmark_example
 
   bazel-integration-tests:
@@ -132,6 +133,7 @@ jobs:
         if: matrix.codspeed-mode != 'off'
         with:
           mode: ${{ matrix.codspeed-mode }}
+          upload-url: https://api.staging.preview.codspeed.io/upload
           run: bazel run //examples/google_benchmark_bazel:my_benchmark --@codspeed_core//:codspeed_mode=${{ matrix.codspeed-mode }} --@codspeed_core//:strict_warnings=on
 
   cmake-build: