Fix minor typos in comments and spec names (#21831)

Dockerfile

app/javascript/mastodon/utils/__tests__/html-test.js

app/workers/post_process_media_worker.rb

lib/mastodon/media_cli.rb

lib/tasks/tests.rake

spec/controllers/admin/confirmations_controller_spec.rb

spec/controllers/concerns/signature_verification_spec.rb

spec/models/account_migration_spec.rb

spec/models/account_spec.rb

spec/models/user_settings/setting_spec.rb

spec/services/activitypub/process_account_service_spec.rb