[ci] convert empty s3 artifacts from error to warning

There are a bunch of valid reasons this could happen (e.g. all builds
failed before running any tests), so it shouldn't cause the workflow to
error. Should probably still warn though if we ever are investigating.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/79397

Approved by: https://github.com/janeyx99
diff --git a/tools/stats/upload_stats_lib.py b/tools/stats/upload_stats_lib.py
index 8062e3e..e7c4e41 100644
--- a/tools/stats/upload_stats_lib.py
+++ b/tools/stats/upload_stats_lib.py
@@ -84,8 +84,9 @@
         paths.append(p)
 
     if not found_one:
-        raise RuntimeError(
-            "Didn't find any test reports in s3, there is probably a bug!"
+        print(
+            "::warning title=s3 artifacts not found::"
+            "Didn't find any test reports in s3, there might be a bug!"
         )
     return paths