Silence _perform method redefinition warning

I'd like to get rid of this noisy warning:

```
sentry-rails-5.26.0/lib/sentry/rails/background_worker.rb:5: warning: method redefined; discarding old _perform
sentry-ruby-5.26.0/lib/sentry/background_worker.rb:74: warning: previous definition of _perform was here
````

Author: viralpraxis

sentry-rails/lib/sentry/rails/background_worker.rb

@@ -2,6 +2,7 @@
 
 module Sentry
   class BackgroundWorker
+    alias :_perform :_perform # Silence method redefinition warning.
     def _perform(&block)
       block.call
     ensure