[NI] Remove lambda coersion to Unit in case of error return type(s)

Coersion to Unit from error type leads to misleading type mismatches:
"expected <expected lambda return type> found Unit", despite no user-provided Unit / empty lambda.
These diagnostics were collected, but not reported before, and that had been disguising the issue for a while.

KT-34729 Fixed

compiler/testData/diagnostics/tests/extensions/extensionMemberInClassObject.fir.kt

@@ -1,4 +1,5 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
+// !WITH_NEW_INFERENCE
 
 interface JPAEntityClass<D> {
     fun <T> T.findByName(s: String): D {null!!}