Fix testdata after advancing LATEST_STABLE to 1.3

This commit contains minor changes in testdata, where test and behavior
change are not related

compiler/testData/diagnostics/testsWithStdLib/smartcasts/letAlwaysChangesToNotNull.kt

@@ -1,7 +1,7 @@
 // KT-9051: Allow smart cast for captured variables if they are not modified
 
 fun foo(y: String) {
-    var x: String? = null
+    var x: String? = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>null<!>
     y.let { x = it }
     x<!UNSAFE_CALL!>.<!>length // Smart cast is not possible
 }