Added rollback migration

db/migrate/20231027084327_change_personal_access_tokens_remove_not_null_expires_at.rb

@@ -3,11 +3,13 @@
 class ChangePersonalAccessTokensRemoveNotNullExpiresAt < Gitlab::Database::Migration[2.1]
   disable_ddl_transaction!
+  CONSTRAINT_NAME = 'check_b8d60815eb'
+
   def up
     remove_not_null_constraint :personal_access_tokens, :expires_at
   end
   def down
-    # There may now be nulls in the table, so we cannot re-add the constraint here.
+    add_not_null_constraint :personal_access_tokens, :expires_at, validate: false, constraint_name: CONSTRAINT_NAME
   end
 end