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

idea/testData/findUsages/kotlin/conventions/unaryMinus.0.kt

@@ -2,10 +2,10 @@
 // OPTIONS: usages
 
 class A(val n: Int) {
-    fun <caret>minus(): A = this
+    operator fun <caret>unaryMinus(): A = this
 }
 
 fun test() {
-    A(1).minus()
+    A(1).unaryMinus()
     -A(1)
 }

idea/testData/findUsages/kotlin/conventions/unaryMinus.results.txt

@@ -1,2 +1,2 @@
 Function call (10: 5) -A(1)
-Function call (9: 10) A(1).minus()
+Function call (9: 10) A(1).unaryMinus()