How can I convert Scala 3.x code with mdoc CLI?

[windymelt]

Hi, thank you for neat and useful software.

My mdoc (v2.6.1) seems not accepting Scala 3.x code from CLI.

For instance, following code does not compile:

```scala mdoc
def fib(n: Int): Int = n match
case 1 => 1
case n => n * fib(n - 1)

fib(5)
```

mdoc --in main.template.md --out main.mdoc.md
info: Compiling 1 file to main.mdoc.md
error: main.template.md:5:1: `{` expected but `case` found
case 1 => 1
^^^^
info: Compiled in 0.2s (1 error)

Can I modify Scala version from CLI?

Of course, creating entire project to compiling just one source code is such a pain...

[tgodzik]

Looks like we never added the option, we were mostly focused on sbt and worksheets. It should not be hard to add though.