fix: use sed instead of head -n-1 for macOS compatibility

The head -n-1 command is invalid on macOS (used in GitHub Actions).
Replace with sed '$d' which removes the last line and works on all systems.

This fixes the HTTP response parsing in the document seeding step.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Teodor Ciuraru

.github/workflows/swift-browserstack.yml

@@ -192,7 +192,7 @@ jobs:
         
         # Extract HTTP status code and response body
         HTTP_CODE=$(echo "$RESPONSE" | tail -n1)
-        BODY=$(echo "$RESPONSE" | head -n-1)
+        BODY=$(echo "$RESPONSE" | sed '$d')
         
         # Check if insertion was successful
         if [ "$HTTP_CODE" -eq 200 ] || [ "$HTTP_CODE" -eq 201 ]; then