CI: revert changes to Docker workflow.

Credentials were removed from repository secrets and that's why login doesn't
work.

This reverts commit c4e244effc.
This reverts commit c8988499dc.

.github/workflows/docker_image.yml

@@ -24,6 +24,9 @@ jobs:
         cd ./scripts
         docker build --tag termux/package-builder:latest .
     - name: Push to hub.docker.com
+      env:
+        DOCKER_LOGIN: xeffyr
+        DOCKER_PASS: ${{ secrets.DOCKER_HUB_PASSWORD }}
       run: |
-        docker login --username xeffyr --password ${{ secrets.DOCKER_HUB_PASSWORD }}
+        docker login --username "${DOCKER_LOGIN}" --password "${DOCKER_PASS}"
         docker push termux/package-builder:latest