Fix tests not unsubscribing from Notifications.

See https://github.com/rails/rails/blob/master/activesupport/lib/active_support/notifications.rb#L131

activerecord/test/cases/adapters/mysql2/connection_test.rb

@@ -4,12 +4,12 @@ class MysqlConnectionTest < ActiveRecord::TestCase
   def setup
     super
     @subscriber = SQLSubscriber.new
-    ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
+    @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
     @connection = ActiveRecord::Base.connection
   end
 
   def teardown
-    ActiveSupport::Notifications.unsubscribe(@subscriber)
+    ActiveSupport::Notifications.unsubscribe(@subscription)
     super
   end
 

activerecord/test/cases/adapters/postgresql/connection_test.rb

@@ -8,12 +8,12 @@ class NonExistentTable < ActiveRecord::Base
     def setup
       super
       @subscriber = SQLSubscriber.new
-      ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
+      @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
       @connection = ActiveRecord::Base.connection
     end
 
     def teardown
-      ActiveSupport::Notifications.unsubscribe(@subscriber)
+      ActiveSupport::Notifications.unsubscribe(@subscription)
       super
     end
 

activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

@@ -23,7 +23,7 @@ def setup
         eosql
 
         @subscriber = SQLSubscriber.new
-        ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
+        @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
       end
 
       def test_bad_connection
@@ -70,7 +70,7 @@ def test_invalid_column
       end
 
       def teardown
-        ActiveSupport::Notifications.unsubscribe(@subscriber)
+        ActiveSupport::Notifications.unsubscribe(@subscription)
         super
       end
 

activerecord/test/cases/bind_parameter_test.rb

@@ -22,11 +22,11 @@ def setup
       @connection = ActiveRecord::Base.connection
       @listener   = LogListener.new
       @pk         = Topic.columns.find { |c| c.primary }
-      ActiveSupport::Notifications.subscribe('sql.active_record', @listener)
+      @subscriber = ActiveSupport::Notifications.subscribe('sql.active_record', @listener)
     end
 
     teardown do
-      ActiveSupport::Notifications.unsubscribe(@listener)
+      ActiveSupport::Notifications.unsubscribe(@subscriber)
     end
 
     if ActiveRecord::Base.connection.supports_statement_cache?