Fix Runner access for programming groups

* We also rename the corresponding columns in the Runner model, so that for polymorphic association gets clear.

db/migrate/20230820182149_rename_user_to_contributor_in_runners.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class RenameUserToContributorInRunners < ActiveRecord::Migration[7.0]
+  def change
+    change_table :runners do |t|
+      t.rename :user_id, :contributor_id
+      t.rename :user_type, :contributor_type
+    end
+  end
+end