Add default value for RepublishingEvents

When we added the `bulk` field in
[`578590b27`](578590b) it seemed to default to `false` when creating new `RepublishingEvent`s without us needing to set a default value.

It appears that before merging this PR, a rubocop update was merged and
the PR branch not rebased with `main` after this. This caused Rubocop to
fail on `main` due to this rubocop issue.

Here we add an explicit `false` default value for `RepublishingEvent`s
and ignore the Rubocop violation on the previous migration.

I've had to use `up` rather than `change` here as `change_column` is not
reversible. According to a comment on the accepted answer on [this Stack
Overflow
post](578590b),

```
If you need reversible migrations, put this in an up block rather
than a change block. You can leave the down block empty. It won't revert
the table to the original condition but the migration can be rolled
back.
```

db/migrate/20240521150403_add_bulk_and_bulk_content_type_to_republishing_events.rb

@@ -1,7 +1,7 @@
 class AddBulkAndBulkContentTypeToRepublishingEvents < ActiveRecord::Migration[7.1]
   def change
     change_table :republishing_events, bulk: true do |t|
-      t.boolean :bulk, null: false
+      t.boolean :bulk, null: false # rubocop:disable Rails/NotNullColumn
       t.integer :bulk_content_type
     end
   end

db/migrate/20240529093425_make_republishing_events_bulk_false_by_default.rb

@@ -0,0 +1,7 @@
+class MakeRepublishingEventsBulkFalseByDefault < ActiveRecord::Migration[7.1]
+  def up
+    change_column :republishing_events, :bulk, :boolean, default: false
+  end
+
+  def down; end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2024_05_21_150403) do
+ActiveRecord::Schema[7.1].define(version: 2024_05_29_093425) do
   create_table "assets", charset: "utf8mb3", force: :cascade do |t|
     t.string "asset_manager_id", null: false
     t.string "variant", null: false
@@ -865,7 +865,7 @@
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "content_id"
-    t.boolean "bulk", null: false
+    t.boolean "bulk", default: false, null: false
     t.integer "bulk_content_type"
     t.index ["user_id"], name: "index_republishing_events_on_user_id"
   end