Merge branch 'gitlab-ci-dind' into 'develop'

GitLab CI: tag `dind`

See merge request soapbox-pub/soapbox!1819

.gitlab-ci.yml

@@ -148,6 +148,8 @@ docker:
   image: docker:20.10.17
   services:
     - docker:20.10.17-dind
+  tags:
+    - dind
   # https://medium.com/devops-with-valentine/how-to-build-a-docker-image-and-push-it-to-the-gitlab-container-registry-from-a-gitlab-ci-pipeline-acac0d1f26df
   script:
     - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin