Resolves#43671.
Bumps the Alpine base image from 3.23.3 to 3.23.4 in the Dockerfiles
that produce published images, picking up patched openssl, musl, and
zlib packages. Follows the same pattern as #38977.
### CVEs resolved
- HIGH: CVE-2026-28388, CVE-2026-28389, CVE-2026-28390, CVE-2026-31790,
CVE-2026-2673, CVE-2026-40200
- MEDIUM: CVE-2026-27171, CVE-2026-6042, CVE-2026-22184
### Test plan
- CI image build passes.
- Trivy/ECR scan on the resulting fleetdm/fleet image confirms the nine
listed CVEs are gone.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Chores**
* Updated Docker base images to Alpine 3.23.4 across infrastructure and
deployment components for improved stability and security.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Sharon Katz
6032c137e5