Remove support for Ubuntu 20.04 and Debian 11.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

.github/workflows/production-suite.yml

@@ -135,11 +135,6 @@ jobs:
         include:
           # Docker images are built from 'tools/ci/Dockerfile'; the comments at
           # the top explain how to build and upload these images.
-          - docker_image: zulip/ci:focal
-            name: Ubuntu 20.04 production install
-            os: focal
-            extra-args: ""
-
           - docker_image: zulip/ci:jammy
             name: Ubuntu 22.04 production install and PostgreSQL upgrade with pgroonga
             os: jammy
@@ -150,11 +145,6 @@ jobs:
             os: noble
             extra-args: ""
 
-          - docker_image: zulip/ci:bullseye
-            name: Debian 11 production install
-            os: bullseye
-            extra-args: ""
-
           - docker_image: zulip/ci:bookworm
             name: Debian 12 production install with custom db name and user
             os: bookworm
@@ -247,15 +237,6 @@ jobs:
         include:
           # Docker images are built from 'tools/ci/Dockerfile.prod'; the comments at
           # the top explain how to build and upload these images.
-          - docker_image: zulip/ci:focal-3.2
-            name: 3.2 Version Upgrade
-            os: focal
-          - docker_image: zulip/ci:bullseye-4.2
-            name: 4.2 Version Upgrade
-            os: bullseye
-          - docker_image: zulip/ci:bullseye-5.0
-            name: 5.0 Version Upgrade
-            os: bullseye
           - docker_image: zulip/ci:jammy-6.0
             name: 6.0 Version Upgrade
             os: jammy

.github/workflows/zulip-ci.yml

@@ -30,18 +30,6 @@ jobs:
         include:
           # Base images are built using `tools/ci/Dockerfile.prod.template`.
           # The comments at the top explain how to build and upload these images.
-          # Ubuntu 20.04 ships with Python 3.8.10.
-          - docker_image: zulip/ci:focal
-            name: Ubuntu 20.04 (Python 3.8, backend)
-            os: focal
-            include_documentation_tests: false
-            include_frontend_tests: false
-          # Debian 11 ships with Python 3.9.2.
-          - docker_image: zulip/ci:bullseye
-            name: Debian 11 (Python 3.9, backend)
-            os: bullseye
-            include_documentation_tests: false
-            include_frontend_tests: false
           # Ubuntu 22.04 ships with Python 3.10.12.
           - docker_image: zulip/ci:jammy
             name: Ubuntu 22.04 (Python 3.10, backend + frontend)
@@ -227,7 +215,7 @@ jobs:
           fi
 
       - name: Test locked requirements
-        if: ${{ matrix.os == 'focal' }}
+        if: ${{ matrix.os == 'jammy' }}
         run: |
           . /srv/zulip-py3-venv/bin/activate && \
           ./tools/test-locked-requirements