BCDA-8187: Update Alpine linux reference in Dockerfile

[alex-dzeda]

🎫 Ticket

https://jira.cms.gov/browse/BCDA-8187

🛠 Changes

Update Alpine distro 3.15-> 3.18

ℹ️ Context for reviewers

Remediates a finding in the ticket above for an unsupported image.

✅ Acceptance Validation

CI flow passes, no longer using outdated version.

🔒 Security Implications

• This PR adds a new software dependency or dependencies.
• This PR modifies or invalidates one or more of our security controls.
• This PR stores or transmits data that was not stored or transmitted before.
• This PR requires additional review of its security implications for other reasons.

If any security implications apply, add Jason Ashbaugh (GitHub username: StewGoin) as a reviewer and do not merge this PR without his approval.