Surround with null check: fix incorrect check for 'in' expression

#KT-31749 Fixed

idea/testData/quickfix/surroundWithNullCheck/in.kt

@@ -0,0 +1,4 @@
+// "Surround with null check" "true"
+fun test(a: String, b: List<String>?) {
+    a <caret>in b
+}

idea/testData/quickfix/surroundWithNullCheck/in.kt.after

@@ -0,0 +1,6 @@
+// "Surround with null check" "true"
+fun test(a: String, b: List<String>?) {
+    if (b != null) {
+        a in b
+    }
+}