Fix Ruby 2.7 deprecation warning in JSON module

In Ruby 3.0, positional arguments and keyword arguments will be
separated. Ruby 2.7 will warn for behaviors that will change in Ruby
3.0. In most cases, you can avoid the incompatibility by adding the
double splat operator. It explicitly specifies passing keyword arguments
instead of a Hash object.

lib/gitlab/json.rb

@@ -22,7 +22,7 @@ module Gitlab
         string = string.to_s unless string.is_a?(String)
 
         legacy_mode = legacy_mode_enabled?(opts.delete(:legacy_mode))
-        data = adapter_load(string, opts)
+        data = adapter_load(string, **opts)
 
         handle_legacy_mode!(data) if legacy_mode