Drop Ubuntu 18.04 devcontainer

Ubuntu 18.04 is EOL now, so stop building devcontainers for it.

Also adjust some dates in the documentation.

.devcontainer/on-create-command.sh

@@ -41,11 +41,5 @@ apt_get_install \
   openssh-server \
   zsh
 
-# Ubuntu 18.04 doesn't include zsh-autosuggestions
-if ! grep -q "Ubuntu 18.04" /etc/issue &>/dev/null
-then
-  apt_get_install zsh-autosuggestions
-fi
-
 # Start the SSH server so that `gh cs ssh` works.
 sudo service ssh start

.devcontainer/ubuntu18.04/devcontainer.json

@@ -1,36 +0,0 @@
-// For format details, see https://aka.ms/devcontainer.json.
-{
-  "name": "Homebrew/brew-ubuntu18.04",
-  "image": "ghcr.io/homebrew/ubuntu18.04:latest",
-
-  "workspaceFolder": "/home/linuxbrew/.linuxbrew/Homebrew",
-  "workspaceMount": "source=${localWorkspaceFolder},target=/home/linuxbrew/.linuxbrew/Homebrew,type=bind,consistency=cached",
-
-  "onCreateCommand": ".devcontainer/on-create-command.sh",
-
-  "customizations": {
-    "vscode": {
-      // Installing all necessary extensions for vscode
-      // Taken from: .vscode/extensions.json
-      "extensions": [
-        "Shopify.ruby-lsp",
-        "sorbet.sorbet-vscode-extension",
-        "github.vscode-github-actions",
-        "anykeyh.simplecov-vscode",
-        "ms-azuretools.vscode-docker",
-        "github.vscode-pull-request-github",
-        "davidanson.vscode-markdownlint",
-        "foxundermoon.shell-format",
-        "timonwong.shellcheck",
-        "ban.spellright",
-        "redhat.vscode-yaml",
-        "koichisasada.vscode-rdbg",
-        "editorconfig.editorconfig"
-      ]
-    }
-  },
-
-  "remoteEnv": {
-    "HOMEBREW_GITHUB_API_TOKEN": "${localEnv:GITHUB_TOKEN}"
-  }
-}

docs/Linux-CI.md

@@ -20,12 +20,16 @@ We plan to proceed with regular updates from 2022 onwards. We aim to use the lat
 
 We will start using the latest Ubuntu LTS version for our CI no earlier than 3 months after its release and, ideally, no more than 12 months after its release.
 
-| Distribution | Glibc | GCC | Usage |
+| Distribution | Glibc | GCC | LTS standard security maintenance |
 |---|---|---|---|
 | Ubuntu 14.04 | 2.19 | 4 | From 2014 to 2017 |
 | Ubuntu 16.04 | 2.23 | 5 | From 2017 to 2022 |
-| Ubuntu 22.04 | 2.35 | 11 | From 2022 to 2024 |
-| Ubuntu 24.04 | ? | ? | From 2024 to 2026 |
+| Ubuntu 20.04 | 2.31 | 5 | From 2020 to 2025 |
+| Ubuntu 22.04 | 2.35 | 11 | From 2022 to 2027 |
+| Ubuntu 24.04 | 2.39 | 13 | From 2024 to 2029 |
+| Ubuntu 26.04 | ? | ? | ? |
+
+[Source](https://ubuntu.com/about/release-cycle)
 
 ## Why always use the latest version?