fix(docker): add libc6-compat for glibc compatibility

[Watakolo]

Summary

Adds libc6-compat to the final Alpine image stage in the Dockerfile.

Problem

Certain third-party CLI tools or custom Terraform providers used by the Burrito runner are compiled against glibc instead of Alpine's native musl. Without libc6-compat, these binaries fail to execute inside the runner container with permission or missing library errors.

Solution

Install libc6-compat via apk in the runner base image.

Impact

• Improves out-of-the-box compatibility for glibc binaries.
• Negligible image size impact (< 50 KB).
• No breaking changes.