[scout] fix missing failed test annotations in BK (#239959)

## Summary

We are removing scout reports to avoid ingesting the same data twice,
but it was also removing failed test artifacts and causing missing
annotations. See this failed
[build](https://buildkite.com/elastic/kibana-on-merge/builds/80159#)

This PR updates the removal logic so that we keep failed test artifacts
to be uploaded and later used for BK annotations.

<img width="1275" height="416" alt="image"
src="https://github.com/user-attachments/assets/ccf10218-5ad4-4649-aa90-d4e9b912915a"
/>

(cherry picked from commit 1a54d44)

Author: dmlemeshko

.buildkite/scripts/steps/test/scout_configs.sh

@@ -100,9 +100,17 @@ upload_events_if_available() {
         echo "⚠️ Upload failed for $config_path ($mode) with exit code $UPLOAD_EXIT_CODE"
       fi
 
-      # Clean up reports directory after upload attempt
-      echo "🧹 Cleaning up Scout reports directory"
-      rm -rf .scout/reports
+      # Clean up events reports to avoid double ingestion, but preserve failure reports
+      echo "🧹 Cleaning up Scout events reports (preserving failure reports for annotations)"
+      # Only remove events reports, not failure reports
+      if [ -d ".scout/reports" ]; then
+        for dir in .scout/reports/scout-playwright-*; do
+          if [ -d "$dir" ] && [[ "$dir" != *"scout-playwright-test-failures-"* ]]; then
+            rm -rf "$dir"
+          fi
+        done
+      fi
+      # Keep .scout/reports/scout-playwright-test-failures-* and .scout/test-artifacts/ for failed test reporter
     else
       echo "❌ No Scout reports found for $config_path ($mode)"
     fi