FIR: Fix inference case with flexible captured types

Previsously, errors have been ignored because we ignored errors raised
from the completion phase

See the comment above the createConstraintPartForLowerBoundAndFlexibleTypeVariable

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ConeInferenceContext.kt

@@ -492,4 +492,7 @@ interface ConeInferenceContext : TypeSystemInferenceExtensionContext, ConeTypeCo
         }
         return intersectionType.withAlternative(secondCandidate)
     }
+
+    override fun SimpleTypeMarker.createConstraintPartForLowerBoundAndFlexibleTypeVariable(): KotlinTypeMarker =
+        createFlexibleType(this.makeSimpleTypeDefinitelyNotNullOrNotNull(), this.withNullability(true))
 }