Bump webpacker from 4.0.7 to 4.2.0 (#12416)

* Bump webpacker from 4.0.7 to 4.2.0

Bumps [webpacker](https://github.com/rails/webpacker) from 4.0.7 to 4.2.0.
- [Release notes](https://github.com/rails/webpacker/releases)
- [Changelog](https://github.com/rails/webpacker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/webpacker/compare/v4.0.7...v4.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

* Use NODE_ENV=tests instead of test, to work around async modules not having a chunk

Gemfile

@@ -93,7 +93,7 @@ gem 'tty-command', '~> 0.9', require: false
 gem 'tty-prompt', '~> 0.19', require: false
 gem 'twitter-text', '~> 1.14'
 gem 'tzinfo-data', '~> 1.2019'
-gem 'webpacker', '~> 4.0'
+gem 'webpacker', '~> 4.2'
 gem 'webpush'
 
 gem 'json-ld', git: 'https://github.com/ruby-rdf/json-ld.git', ref: 'e742697a0906e74e8bb777ef98137bc3955d981d'