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

compiler/testData/codegen/box/defaultArguments/function/augmentedAssignment.kt

@@ -2,7 +2,7 @@ var result = "Fail"
 
 class A
 
-fun A.plusAssign(a: A, s: String = "OK") {
+operator fun A.plusAssign(a: A, s: String = "OK") {
     result = s
 }
 

compiler/testData/codegen/box/defaultArguments/function/augmentedAssignmentViaBinaryExpression.kt

@@ -2,7 +2,7 @@ var result = "Fail"
 
 class A
 
-fun A.plus(a: A, s: String = "OK"): A {
+operator fun A.plus(a: A, s: String = "OK"): A {
     result = s
     return this
 }

compiler/testData/codegen/box/defaultArguments/function/binaryCall.kt

@@ -1,3 +1,3 @@
-fun Int.foo(o: String, k: String = "K") = o + k
+infix fun Int.foo(o: String, k: String = "K") = o + k
 
 fun box() = 42 foo "O"

compiler/testData/codegen/box/defaultArguments/function/binaryExpression.kt

@@ -1,5 +1,5 @@
 class A
 
-fun A.plus(i: A, ok: String = "OK") = ok
+operator fun A.plus(i: A, ok: String = "OK") = ok
 
 fun box() = A() + A()

compiler/testData/codegen/box/defaultArguments/function/contains.kt

@@ -1,5 +1,5 @@
 class A
 
-fun A.contains(i: A, actual: Boolean = true) = actual
+operator fun A.contains(i: A, actual: Boolean = true) = actual
 
 fun box() = if (A() in A()) "OK" else "Fail"