fix: Docker Image push to GitHub Container Registry

[maximearmstrong]

Summary:

Fixes #150: Docker image push to GitHub Container Registry is failing

This PR replaces the Personal Access Token (PAT) used in the docker.yml workflow with a GitHub Token. According to GitHub, PATs used to authenticate to ghcr.io should be avoided.

Along with the changes made in this PR, the steps shown here were followed so that the package could access the GitHub token.

Expected behavior:

The Docker Image push to GitHub Container Registry should work properly.

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[maximearmstrong]

Thanks @maximearmstrong! I guess we will see if this works when this PR is merged.

It worked! 🎉