Fix incorrect variable usage in backtrace handling

Corrected the use of the `error.backtrace` variable to `backtrace` in `lib/solid_errors/subscriber.rb` to ensure proper handling of backtrace data.

Author: imageaid

lib/solid_errors/subscriber.rb

@@ -43,7 +43,7 @@ def report(error, handled:, severity:, context:, source: nil)
 
       SolidErrors::Occurrence.create(
         error_id: record.id,
-        backtrace: error.backtrace&.join("\n"),
+        backtrace: backtrace&.join("\n"),
         context: s(context)
       )
     end