Spurious "Type A escapes through type List[A] inferred for the result of the if statement."

I've seen this multiple times locally, but thought that it's a LSP-related issue.

But now it seems to have broken the build on `master`:
https://github.com/effekt-lang/effekt/actions/runs/13927195740/job/38974717008#step:11:932

For posterity, here's an excerpt from the log:
```
==> X effekt.JavaScriptTests.examples/neg/multiple_main.effekt (js) 1.961s munit.FailException: /home/runner/work/effekt/effekt/effekt/jvm/src/test/scala/effekt/EffektTests.scala:145
144: |----------------------------------------------
145: |${ messages.map(m => messaging.formatMessage(m)).distinct.mkString("\n\n") }""".stripMargin)
146:
Error: ot find an message [error] line 1: Multiple main functions

Compilation resulted in the following messages
----------------------------------------------
Error: /home/runner/work/effekt/effekt/libraries/common/list.effekt:382:3: Type A escapes through type List[A] inferred for the result of the if statement.

Error: /home/runner/work/effekt/effekt/libraries/common/list.effekt:382:3: Cannot compile dependency: /home/runner/work/effekt/effekt/libraries/common/list
```

and here's where the error comes from, line 382 is `if (n <= 0) {`
https://github.com/effekt-lang/effekt/blob/55e373b537fcf104419b5ec3685a09e1faa2a5e6/libraries/common/list.effekt#L381-L387