Update test cases for @mainactor inference

Author: DougGregor

test/IDE/print_ast_tc_decls.swift

@@ -536,7 +536,7 @@ class d0170_TestAvailability {
 // PASS_COMMON-LABEL: {{^}}@objc class d0180_TestIBAttrs {{{$}}
 
   @IBAction func anAction(_: AnyObject) {}
-// PASS_COMMON-NEXT: {{^}}  @objc @IBAction func anAction(_: AnyObject){{$}}
+// PASS_COMMON-NEXT: {{^}}  @objc @IBAction @MainActor func anAction(_: AnyObject){{$}}
 
   @IBSegueAction func aSegueAction(_ coder: AnyObject, sender: AnyObject, identifier: AnyObject?) -> Any? { fatalError() }
 // PASS_COMMON-NEXT: {{^}}  @objc @IBSegueAction func aSegueAction(_ coder: AnyObject, sender: AnyObject, identifier: AnyObject?) -> Any?{{$}}

test/attr/attr_objc.swift

@@ -1868,7 +1868,7 @@ class HasIBOutlet {
 // CHECK-LABEL: {{^}}class HasIBAction {
 class HasIBAction {
   @IBAction func goodAction(_ sender: AnyObject?) { }
-  // CHECK: {{^}}  @objc @IBAction func goodAction(_ sender: AnyObject?) {
+  // CHECK: {{^}}  @objc @IBAction @MainActor func goodAction(_ sender: AnyObject?) {
 
   @IBAction func badAction(_ sender: PlainStruct?) { }
   // expected-error@-1{{method cannot be marked @IBAction because the type of the parameter cannot be represented in Objective-C}}