Add test for Schema

We need to create the db table for FlipFlop feature
flagging.

(We add the `Flipflop.show_all_content_block_types?` back in
to the `Schema` model now we understand that the dependency
on FlipFlop is deep.)

Author: edavey

app/models/content_block_manager/content_block/schema.rb

@@ -10,7 +10,7 @@ class Schema
 
       class << self
         def valid_schemas
-          VALID_SCHEMAS
+          Flipflop.show_all_content_block_types? ? VALID_SCHEMAS : %w[pension]
         end
 
         def all

db/migrate/20250821161900_create_flipflop_features.rb

@@ -0,0 +1,11 @@
+class CreateFlipflopFeatures < ActiveRecord::Migration[8.0]
+  def change
+    create_table :flipflop_features do |t|
+      t.text :key, null: false
+      t.boolean :enabled, null: false, default: false
+
+      t.timestamps
+    end
+    add_index :flipflop_features, :key
+  end
+end