K2: don't report RETURN_TYPE_MISMATCH on last statement returns

#KT-53198 Fixed

compiler/testData/diagnostics/testsWithStdLib/functionLiterals/nullableUnitLiteral.fir.kt

@@ -0,0 +1,10 @@
+// FULL_JDK
+
+fun test() {
+    val closeable: java.io.Closeable? = null
+    val closeF = fun() { closeable?.close() }
+    val closeFB = fun(): Unit = <!RETURN_TYPE_MISMATCH!>closeable?.close()<!>
+    val closeFR = fun() { return <!RETURN_TYPE_MISMATCH!>closeable?.close()<!> }
+    val closeL = { closeable?.close() }
+    val closeLR = label@ { return@label closeable?.close() }
+}

compiler/testData/diagnostics/testsWithStdLib/functionLiterals/nullableUnitLiteral.kt

@@ -0,0 +1,10 @@
+// FULL_JDK
+
+fun test() {
+    val closeable: java.io.Closeable? = null
+    val closeF = fun() { closeable?.close() }
+    val closeFB = fun(): Unit = <!TYPE_MISMATCH!>closeable?.close()<!>
+    val closeFR = fun() { return <!TYPE_MISMATCH!>closeable?.close()<!> }
+    val closeL = { closeable?.close() }
+    val closeLR = label@ { return@label closeable?.close() }
+}

compiler/testData/diagnostics/testsWithStdLib/functionLiterals/nullableUnitLiteral.txt

@@ -0,0 +1,3 @@
+package
+
+public fun test(): kotlin.Unit