pandoc-3.11: test/command/11810.md

```
% pandoc -f html -t native
<pre>alpha
    beta
        gamma</pre>
^D
[ Plain
    [ Str "alpha"
    , LineBreak
    , Str "\160\160\160\160beta"
    , LineBreak
    , Str "\160\160\160\160\160\160\160\160gamma"
    ]
]
```