Improve check for GC.stat(:total_allocated_objects)

* This works whether the Ruby implementation raises or uses a Hash with
  a default of 0 to represent unknown keys (like TruffleRuby) and so
  this is more portable.
* Also avoids an extra exception on JRuby.

Author: eregon

activesupport/lib/active_support/notifications/instrumenter.rb

@@ -158,16 +158,14 @@ def now_cpu # rubocop:disable Lint/DuplicateMethods
           end
         end
 
-        begin
-          GC.stat(:total_allocated_objects)
-        rescue ArgumentError # Likely on JRuby
+        if GC.stat.key?(:total_allocated_objects)
           def now_allocations
-            0
-          end
-        else
-          def now_allocations  # rubocop:disable Lint/DuplicateMethods
             GC.stat(:total_allocated_objects)
           end
+        else # Likely on JRuby, TruffleRuby
+          def now_allocations
+            0
+          end
         end
     end
   end