Add latest tag

Author: williamdes

.github/workflows/publish.yml

@@ -30,5 +30,5 @@ jobs:
                   # See: https://github.com/docker/buildx/issues/59
                   ACTION: push
                   DOCKER_BUILDKIT: 1
-                  IMAGE_TAG: docker.io/botsudo/phpunit
+                  IMAGE_TAG: docker.io/botsudo/phpunit:latest
                   PLATFORM: linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/ppc64le,linux/s390x