run apk upgrade in Dockerfile

[matheusfm]

Description

This PR adds a layer in Dockerfile for running apk upgrade to fix known vulnerabilities.

TAG=test make docker-build
trivy image ghcr.io/undistro/marvin:test --scanners vuln --vuln-type os

2024-04-26T15:44:39.295-0300    INFO    Vulnerability scanning is enabled
2024-04-26T15:44:40.105-0300    INFO    Detected OS: alpine
2024-04-26T15:44:40.106-0300    INFO    Detecting Alpine vulnerabilities...

ghcr.io/undistro/marvin:test (alpine 3.19.1)

Total: 0 (UNKNOWN: 0, LOW: 0, MEDIUM: 0, HIGH: 0, CRITICAL: 0)

How has this been tested?

• make docker-build

Checklist

• I have labeled this PR with the relevant Type labels
• I have documented my code (if applicable)
• My changes are covered by tests