Move gallery native UI test launching out of test and into setup (#97177)

dev/integration_tests/flutter_gallery/ios/GalleryUITests/GalleryUITests.m

@@ -5,20 +5,22 @@
 #import <XCTest/XCTest.h>
 
 @interface GalleryUITests : XCTestCase
+@property (strong) XCUIApplication *app;
 @end
 
 @implementation GalleryUITests
 
 - (void)setUp {
     self.continueAfterFailure = NO;
-}
 
-- (void)testLaunch {
     XCUIApplication *app = [[XCUIApplication alloc] init];
     [app launch];
+    self.app = app;
+}
 
+- (void)testLaunch {
     // Basic smoke test that the app launched and any element was loaded.
-    XCTAssertTrue([app.otherElements.firstMatch waitForExistenceWithTimeout:60.0]);
+    XCTAssertTrue([self.app.otherElements.firstMatch waitForExistenceWithTimeout:60.0]);
 }
 
 @end