Bump apps/frontend from `873e57c` to `9b9c91a`
Bump apps/frontend from `873e57c` to `9b9c91a`

Bumps [apps/frontend](https://github.com/alphagov/frontend) from `873e57c` to `9b9c91a`.
- [Release notes](https://github.com/alphagov/frontend/releases)
- [Commits](https://github.com/alphagov/frontend/compare/873e57c3c592153574eb0e034957cbbaaf5ab24a...9b9c91a4842f21b2b9eceeaab813827b942dbde8)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
eliotsykes/real-world-rails