ci: allow image builds and ci-test bootstrap egress

[komer3]

Summary

• allow index.docker.io:443 for the image workflow under harden-runner block
• allow the Jetify and Nix bootstrap endpoints needed by ci-test to install devbox under block

Why

• the image workflow was blocked when ko reached index.docker.io/v2
• the ci-test failures were not stale-cache related; harden-runner logs showed blocked hosts in the devbox bootstrap path: releases.jetify.com, releases.jetpack.io, get.jetify.com, get.jetpack.io, artifacts.nixos.org, cache.nixos.org
• a manual workflow_dispatch run on this branch now passes end-to-end: https://github.com/linode/karpenter-provider-linode/actions/runs/25400671340

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.42%. Comparing base (7b6f50a) to head (46a0cb7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   75.42%   75.42%           
=======================================
  Files          38       38           
  Lines        2828     2828           
=======================================
  Hits         2133     2133           
  Misses        508      508           
  Partials      187      187           

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[komer3]

Fixed ci-test workflow run: https://github.com/linode/karpenter-provider-linode/actions/runs/25400671340