Fix GHCR authentication in netconf-simulator publish workflow

Correct the GitHub Actions workflow to use docker/login-action@v3 for proper
authentication to GitHub Container Registry.
Previously, the workflow attempted to pass the token directly via docker login,
causing authentication failures.

JIRA: LIGHTY-385
Signed-off-by: tobias.pobocik tobias.pobocik@pantheon.tech
Signed-off-by: tobias.pobocik <tobias.pobocik@pantheon.tech>

Author: Tobianas

.github/workflows/publish-simulator.yml

@@ -67,7 +67,7 @@ jobs:
       - name: Docker log in (ghcr.io)
         shell: bash
         run: |
-          echo ${{ inputs.publish-access-key}} | docker login  --username ${{ github.actor }} --password-stdin ghcr.io
+          echo ${{ env.PUBLISH_ACCESS_KEY }} | docker login --username ${{ github.actor }} --password-stdin ghcr.io
       - name: Publish docker image (ghcr.io)
         shell: bash
         run: |