ci: fix permissions for publishing charts

[shvbsle]

Issue #, if available:
CI for publishing charts failing with:
https://github.com/aws/eks-node-monitoring-agent/actions/runs/19902689831/job/57050675940

Run hack/publish-charts.sh
Successfully packaged chart and saved it to: /home/runner/work/eks-node-monitoring-agent/eks-node-monitoring-agent/eks-node-monitoring-agent-1.4.2.tgz
fatal: path '/home/runner/work/eks-node-monitoring-agent/eks-node-monitoring-agent/eks-node-monitoring-agent-1.4.2.tgz' exists on disk, but not in 'origin/gh-pages'
/home/runner/work/eks-node-monitoring-agent/eks-node-monitoring-agent/eks-node-monitoring-agent-1.4.2.tgz
Switched to a new branch 'gh-pages'
branch 'gh-pages' set up to track 'origin/gh-pages'.
[gh-pages f0b0edb] Publish charts 8c55e64
 2 files changed, 20 insertions(+), 5 deletions(-)
 create mode 100644 eks-node-monitoring-agent-1.4.2.tgz
remote: Permission to aws/eks-node-monitoring-agent.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/aws/eks-node-monitoring-agent/': The requested URL returned error: 403
Error: Process completed with exit code 128.

Description of changes:
Attempting to fix permissions

Testing Done:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.