Wrong diagnostic when last expression in lambda contains assignment operation

#KT-6769 Fixed

compiler/testData/diagnostics/tests/functionLiterals/assignmentOperationInLambda.kt

@@ -0,0 +1,16 @@
+fun test(bal: Array<Int>) {
+    var bar = 4
+
+    val a = { bar += 4 }
+    a : () -> Unit
+
+    val b = { bar = 4 }
+    b : () -> Unit
+
+    val c = { bal[2] = 3 }
+    c : () -> Unit
+
+    val d = run { bar += 4 }
+    d : Unit
+}
+fun <T> run(f: () -> T): T = f()