Increase integration_test package minimum iOS version to 9.0 (flutter#89621)

Author: jmagman

packages/integration_test/ios/integration_test.podspec

@@ -20,6 +20,6 @@ LICENSE
   s.dependency 'Flutter'
   s.ios.framework  = 'UIKit'
 
-  s.platform = :ios, '8.0'
+  s.platform = :ios, '9.0'
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }
 end