FIR: return Unit from empty lambda

compiler/fir/analysis-tests/testData/resolveWithStdlib/problems/invokePriority.txt

@@ -6,7 +6,7 @@ FILE: invokePriority.kt
 
         public final fun bar(): R|kotlin/Unit| {
             lval foo: R|kotlin/String.() -> kotlin/Unit| = fun R|kotlin/String|.<anonymous>(): R|kotlin/Unit| {
-                Unit
+                ^ Unit
             }
 
             local final fun R|kotlin/String|.foo(): R|kotlin/Unit| {
@@ -26,7 +26,7 @@ FILE: invokePriority.kt
         }
 
         public final val foo: R|kotlin/String.() -> kotlin/Unit| = fun R|kotlin/String|.<anonymous>(): R|kotlin/Unit| {
-            Unit
+            ^ Unit
         }
 
             public get(): R|kotlin/String.() -> kotlin/Unit|
@@ -65,7 +65,7 @@ FILE: invokePriority.kt
             }
 
             public final val f: R|() -> kotlin/Unit| = fun <anonymous>(): R|kotlin/Unit| {
-                Unit
+                ^ Unit
             }
 
                 public get(): R|() -> kotlin/Unit|