[QA] Fix a 'superclass must be a Class' error

Signed-off-by: Rémy Coutable <remy@rymai.me>

qa/qa/scenario/test/integration/github.rb

@@ -2,7 +2,7 @@ module QA
   module Scenario
     module Test
       module Integration
-        class Github < Test::Instance
+        class Github < Test::Instance::All
           tags :github
 
           def perform(address, *rspec_options)

qa/qa/scenario/test/integration/kubernetes.rb

@@ -2,7 +2,7 @@ module QA
   module Scenario
     module Test
       module Integration
-        class Kubernetes < Test::Instance
+        class Kubernetes < Test::Instance::All
           tags :kubernetes
         end
       end

qa/qa/scenario/test/integration/ldap.rb

@@ -2,7 +2,7 @@ module QA
   module Scenario
     module Test
       module Integration
-        class LDAP < Test::Instance
+        class LDAP < Test::Instance::All
           tags :ldap
         end
       end

qa/qa/scenario/test/integration/mattermost.rb

@@ -6,7 +6,7 @@ module QA
         # Run test suite against any GitLab instance where mattermost is enabled,
         # including staging and on-premises installation.
         #
-        class Mattermost < Test::Instance
+        class Mattermost < Test::Instance::All
           tags :core, :mattermost
 
           def perform(address, mattermost, *rspec_options)