ci: Switch to hosting the CI images under Zulip on Dockerhub.

.github/workflows/production-suite.yml

@@ -36,7 +36,7 @@ jobs:
     # This docker image was created by a generated Dockerfile at:
     #   tools/ci/images/bionic/Dockerfile
     # Bionic ships with Python 3.6.
-    container: amanagr/actions:bionic
+    container: zulip/ci:bionic
     steps:
       - name: Add required permissions
         run: |
@@ -110,17 +110,17 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - docker_image: amanagr/actions:bionic
+          - docker_image: zulip/ci:bionic
             name: Bionic production install
             is_bionic: true
             os: bionic
 
-          - docker_image: amanagr/actions:focal
+          - docker_image: zulip/ci:focal
             name: Focal production install
             is_focal: true
             os: focal
 
-          - docker_image: ligmitz/actions:buster
+          - docker_image: zulip/ci:buster
             name: Buster production install
             is_buster: true
             os: buster

.github/workflows/zulip-ci.yml

@@ -19,7 +19,7 @@ jobs:
           # This docker image was created by a generated Dockerfile at:
           #   tools/ci/images/bionic/Dockerfile
           # Bionic ships with Python 3.6.
-          - docker_image: amanagr/actions:bionic
+          - docker_image: zulip/ci:bionic
             name: Ubuntu 18.04 Bionic (Python 3.6, backend + frontend)
             os: bionic
             is_bionic: true
@@ -28,7 +28,7 @@ jobs:
           # This docker image was created by a generated Dockerfile at:
           #   tools/ci/images/focal/Dockerfile
           # Focal ships with Python 3.8.2.
-          - docker_image: amanagr/actions:focal
+          - docker_image: zulip/ci:focal
             name: Ubuntu 20.04 Focal (Python 3.8, backend)
             os: focal
             is_focal: true

tools/ci/Dockerfile.template

@@ -22,10 +22,8 @@
 
 # To rebuild from this file for a given release, say bionic:
 #   0. $ tools/ci/generate-dockerfiles
-#   1. pick a new image name, like `gregprice/actions:bionic`
-#   2. $ sudo docker build tools/ci/images/$RELEASE/ --tag $NAME
-#   3. $ sudo docker push $NAME
-#   4. update .github/workflows/zulip-ci.yml to refer to the new name
+#   1. $ sudo docker build tools/ci/images/$RELEASE/ --tag zulip/ci:$RELEASE
+#   2. $ sudo docker push zulip/ci:$RELEASE
 
 FROM {base_image}