fix(yabeda): Replace endless method syntax for Ruby 2.7 compatibility

Endless method syntax (def m() = val) requires Ruby 3.0+. Replace with
conventional empty method bodies (def m; end) so RuboCop using the Ruby
2.7 parser does not reject the file.

Co-Authored-By: Claude Sonnet 4.6 <noreply@example.com>

Author: dingsdax

sentry-yabeda/lib/sentry/yabeda/adapter.rb

@@ -6,10 +6,10 @@ module Sentry
   module Yabeda
     class Adapter < ::Yabeda::BaseAdapter
       # Sentry does not require pre-registration of metrics
-      def register_counter!(_metric) = nil
-      def register_gauge!(_metric) = nil
-      def register_histogram!(_metric) = nil
-      def register_summary!(_metric) = nil
+      def register_counter!(_metric); end
+      def register_gauge!(_metric); end
+      def register_histogram!(_metric); end
+      def register_summary!(_metric); end
 
       def perform_counter_increment!(counter, tags, increment)
         return unless enabled?