ci: Use GitHub Container Registery images tagged 2021

Previously (and implicitly) used "latest". The tag 2021 is new today, the
image contents have not changed since they were generated in 2021.

They have moved container registry twice since 2021
- #791 Docker -> Amazon Elastic Container Registry (public.ecr.aws/n5z0e8q)
- #1128 Amazon ECR -> GitHub Container Registry (ghcr.io/mitogen-hq)

This commit also removes the last references to ECR.

.ci/ci_lib.py

@@ -39,7 +39,7 @@ DISTRO_SPECS = os.environ.get(
 IMAGE_PREP_DIR = os.path.join(GIT_ROOT, 'tests/image_prep')
 IMAGE_TEMPLATE = os.environ.get(
     'MITOGEN_TEST_IMAGE_TEMPLATE',
-    'public.ecr.aws/n5z0e8q9/%(distro)s-test',
+    'ghcr.io/mitogen-hq/%(distro)s-test:2021',
 )
 TESTS_SSH_PRIVATE_KEY_FILE = os.path.join(GIT_ROOT, 'tests/data/docker/mitogen__has_sudo_pubkey.key')
 
@@ -227,7 +227,7 @@ def container_specs(
     [{'distro': 'debian11',
       'family': 'debian',
       'hostname': 'localhost',
-      'image': 'public.ecr.aws/n5z0e8q9/debian11-test',
+      'image': 'ghcr.io/mitogen-hq/debian11-test:2021',
       'index': 1,
       'name': 'target-debian11-1',
       'port': 2201,
@@ -235,7 +235,7 @@ def container_specs(
      {'distro': 'centos6',
       'family': 'centos',
       'hostname': 'localhost',
-      'image': 'public.ecr.aws/n5z0e8q9/centos6-test',
+      'image': 'ghcr.io/mitogen-hq/centos6-test:2021',
       'index': 2,
       'name': 'target-centos6-2',
       'port': 2202,

.github/workflows/tests.yml

@@ -8,11 +8,6 @@ on:
     branches-ignore:
       - docs-master
 
-env:
-  #ANSIBLE_VERBOSITY: 3
-  #MITOGEN_LOG_LEVEL: DEBUG
-  MITOGEN_TEST_IMAGE_TEMPLATE: "ghcr.io/mitogen-hq/%(distro)s-test"
-
 # https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners
 # https://github.com/actions/runner-images/blob/main/README.md#software-and-image-support
 jobs:

tests/testlib.py

@@ -57,7 +57,7 @@ DISTRO_SPECS = os.environ.get(
 )
 IMAGE_TEMPLATE = os.environ.get(
     'MITOGEN_TEST_IMAGE_TEMPLATE',
-    'public.ecr.aws/n5z0e8q9/%(distro)s-test',
+    'ghcr.io/mitogen-hq/%(distro)s-test:2021',
 )
 
 TESTS_DIR =                     os.path.join(os.path.dirname(__file__))