mdoc:fail behaving weirdly

[erikerlandson]

@armanbilge I am seeing weird behaviors for mdoc code blocks where error (:fail) is expected.

It is behaving as if it is keeping a previous error message instead of reporting the actual error message:

That error is from previous fail demo with a deliberately bad Quantity expression, instead of the error for 7 + false

[erikerlandson]

All the code blocks that compile correctly seem to be rendering fine.

[armanbilge]

That is really really strange 🤔 I don't think I've used the :fail modifier so I can't think why it might do that. If you can minimize it seems like a bug. It might even be Scala 3 specific since that's a new compiler and perhaps this part of the mdoc/Scala 3 integration hasn't been tested.

[erikerlandson]

I'll file an issue for mdoc, but here is a minimal example

```scala mdoc:fail
val nope = "foo" * "goo"
```

```scala mdoc:fail
val bad = "moo" * "loo"
```

[erikerlandson]

xref: scalameta/mdoc#663

[erikerlandson]

scalameta/mdoc#664 Fixes this - I am building with a snapshot to pick it up until it makes it into a release