class OldMigrationsRemoved < ActiveRecord::Migration
  def up
    message = "You haven't updated your dev environment in a long time! " \
              "Legacy migration files before 2019 have now been removed. " \
              "Run `rails db:schema:load` before running `rails db:migrate`."
    raise StandardError, message
  end
end

class OldMigrationsRemoved < ActiveRecord::Migration
  def up
    raise StandardError, <<-MESSAGE

      You haven't updated your dev environment in a long time!
      Legacy migration files before 2019 have now been removed.
      Run `rails db:schema:load` before running `rails db:migrate`.

    MESSAGE
  end
end

Format and indent migration message
Format and indent migration message

It's much clearer to read this way:

```
==  OldMigrationsRemoved: migrating ===========================================
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

      You haven't updated your dev environment in a long time!
      Legacy migration files before 2019 have now been removed.
      Run `rails db:schema:load` before running `rails db:migrate`.

```
