Fix tests: "infix modifier required" and "operator modifier required" errors

idea/testData/intentions/infixCallToOrdinary/nullAssertedCall.kt

@@ -1,3 +1,5 @@
+infix fun String.compareTo(other: String) = 0
+
 fun foo(x: String) {
     x!! <caret>compareTo "1"
 }