Update Rack version, fix bundle audit

[rjohnson2011]

Updates Rack version as per the solution to the bundle audit failure below.
Appearing in all PRs during the listing CI check, for example -> https://github.com/department-of-veterans-affairs/vets-api/actions/runs/13685598555/job/38268190857?pr=21080

Logs below:

Run bundle exec bundle-audit check --update --ignore CVE-2024-27456
Download ruby-advisory-db ...
Cloning into '/home/runner/.local/share/ruby-advisory-db'...
ruby-advisory-db:
  advisories:	9[6](https://github.com/department-of-veterans-affairs/vets-api/actions/runs/13685598555/job/38268190857?pr=21080#step:4:7)5 advisories
  last updated:	2025-03-05 12:12:15 -0800
  commit:	8ab1b435ef4029c64d694839e618bd[7](https://github.com/department-of-veterans-affairs/vets-api/actions/runs/13685598555/job/38268190857?pr=21080#step:4:8)375109a6b
Name: rack
Version: 2.2.11
CVE: CVE-2025-27111
GHSA: GHSA-[8](https://github.com/department-of-veterans-affairs/vets-api/actions/runs/13685598555/job/38268190857?pr=21080#step:4:9)cgq-6mh2-7j6v
Criticality: Unknown
URL: https://github.com/rack/rack/security/advisories/GHSA-8cgq-6mh2-7j6v
Title: Escape Sequence Injection vulnerability in Rack lead to Possible Log Injection
Solution: update to '~> 2.2.12', '~> 3.0.13', '>= 3.1.[11](https://github.com/department-of-veterans-affairs/vets-api/actions/runs/13685598555/job/38268190857?pr=21080#step:4:12)'

Vulnerabilities found!
Error: Process completed with exit code 1.