[FIR] Fix determining coercion to Unit

compiler/testData/codegen/box/closures/capturedVarsOptimization/capturedInInlineOnlyAssign.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 
 fun box(): String {

compiler/testData/codegen/box/closures/capturedVarsOptimization/capturedInInlineOnlyCAO.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 
 fun box(): String {

compiler/testData/codegen/box/properties/lateinit/local/localLateinit.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun box(): String {
     lateinit var ok: String
     run {

compiler/testData/codegen/box/properties/lateinit/topLevel/topLevelLateinit.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 lateinit var ok: String
 
 fun box(): String {

compiler/testData/codegen/box/synchronized/changeMonitor.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 
 // WITH_RUNTIME

compiler/testData/ir/irText/classes/initValInLambda.fir.txt

@@ -16,12 +16,12 @@ FILE fqName:<root> fileName:/initValInLambda.kt
               receiver: GET_VAR '<this>: <root>.TestInitValInLambdaCalledOnce declared in <root>.TestInitValInLambdaCalledOnce.<get-x>' type=<root>.TestInitValInLambdaCalledOnce origin=null
     ANONYMOUS_INITIALIZER isStatic=false
       BLOCK_BODY
-        CALL 'public final fun run <T, R> (block: kotlin.Function1<T of kotlin.run, R of kotlin.run>): R of kotlin.run [inline] declared in kotlin' type=kotlin.Nothing origin=null
+        CALL 'public final fun run <T, R> (block: kotlin.Function1<T of kotlin.run, R of kotlin.run>): R of kotlin.run [inline] declared in kotlin' type=kotlin.Unit origin=null
           <T>: kotlin.Int
-          <R>: kotlin.Nothing
+          <R>: kotlin.Unit
           $receiver: CONST Int type=kotlin.Int value=1
-          block: FUN_EXPR type=kotlin.Function1<kotlin.Int, kotlin.Nothing> origin=LAMBDA
-            FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> ($receiver:kotlin.Int) returnType:kotlin.Nothing
+          block: FUN_EXPR type=kotlin.Function1<kotlin.Int, kotlin.Unit> origin=LAMBDA
+            FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> ($receiver:kotlin.Int) returnType:kotlin.Unit
               $receiver: VALUE_PARAMETER name:<this> type:kotlin.Int
               BLOCK_BODY
                 SET_FIELD 'FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.Int visibility:private [final]' type=kotlin.Unit origin=null