Merge branch 'api-simplify-variables-validation' into 'master'

Simplify variables validation in triggers API

See merge request !9506

lib/api/triggers.rb

@@ -21,16 +21,11 @@ module API
         unauthorized! unless trigger.project == project
 
         # validate variables
-        variables = params[:variables]
-        if variables
+        variables = params[:variables].to_h
         unless variables.all? { |key, value| key.is_a?(String) && value.is_a?(String) }
           render_api_error!('variables needs to be a map of key-valued strings', 400)
         end
 
-          # convert variables from Mash to Hash
-          variables = variables.to_h
-        end
-
         # create request and trigger builds
         trigger_request = Ci::CreateTriggerRequestService.new.execute(project, trigger, params[:ref].to_s, variables)
         if trigger_request