Use `JSON` in Helm3Client

`Gitlab::Json` uses `Oj` adapter.
Since Helm3Client is used without all the Gitlab dependencies,
Oj is not defined.

tooling/lib/tooling/helm3_client.rb

@@ -3,7 +3,6 @@
 require 'time'
 require 'json'
 require_relative '../../../lib/gitlab/popen' unless defined?(Gitlab::Popen)
-require_relative '../../../lib/gitlab/json' unless defined?(Gitlab::Json)
 
 module Tooling
   class Helm3Client
@@ -67,7 +66,7 @@ module Tooling
         %(--output json),
         *args
       ]
-      releases = Gitlab::Json.parse(run_command(command))
+      releases = JSON.parse(run_command(command)) # rubocop:disable Gitlab/Json
 
       releases.map do |release|
         Release.new(*release.values_at(*RELEASE_JSON_ATTRIBUTES))