Build docker image and push to GPR with GitHub Actions

docker-build-publish.yaml

name: Build and publish Jekyll Docker image for Octocat Generator
on: [push]
jobs:

  build:
    name: Build
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@master
    - name: clean up, docker login && docker build && docker push
      env:
        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        GPR_PAT: ${{ secrets.GPR_PAT }}
      run: |
        ./cleanup.sh
        docker login -u ${GITHUB_ACTOR} -p ${GPR_PAT} docker.pkg.github.com
        docker build -t docker.pkg.github.com/${GITHUB_REPOSITORY}/octocat-generator:v-${GITHUB_SHA} .
        curl -s -H "Authorization: Token ${GITHUB_TOKEN}" -H "Accept: application/json" -H "Content-type: application/json" -X POST -d "{ \"ref\": \"refs/tags/v-${GITHUB_SHA}\", \"sha\": \"${GITHUB_SHA}\"}" https://api.github.com/repos/${GITHUB_REPOSITORY}/git/refs
        docker push docker.pkg.github.com/${GITHUB_REPOSITORY}/octocat-generator:v-${GITHUB_SHA}

And that curl line is about creating a tag?

Yes, to associate the created docker image with a specific tag