T05: shell integration for zsh, bash, fish, PowerShell; installed at start

.github/workflows/ci.yml

@@ -35,6 +35,7 @@ jobs:
       # The Linux job container runs as root, which ignores the file permissions the tests check.
       - if: runner.os == 'Linux'
         run: |
+          apt-get update && apt-get install -y zsh fish
           useradd --create-home ci
           chmod o+x "$HOME"
           chown -R ci "$GITHUB_WORKSPACE" "$HOME/.cargo" "$HOME/.rustup"