Restore test

[som-snytt]

Fixes #19542

Just restores the test. I thought I had more to verify about exception handling.

[som-snytt]

Annoying line number diff, so I removed the check file.

[som-snytt]

Ah, I noticed this failure but shrugged.

It's worth saying that "tests covering the unexpected" are great, but "test failures unrelated to anything" are corrosive.

Unsuccessful best-effort compilation.
Some best-effort tasty files will not be generated.
Cause:
 java.lang.AssertionError: assertion failed: unresolved symbols: object Fix (line 2) #4290 when pickling tests/neg/i8984.scala
Stack trace: 
 scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:10)
 dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:966)