(Example iOS): Fix microphone permission not being granted

For some reason, iOS now requires this extra step to ensure that the microphone permission
works as intended.

Author: vickz84259

example/push_notifications/ios/Podfile

@@ -37,5 +37,14 @@ end
 post_install do |installer|
   installer.pods_project.targets.each do |target|
     flutter_additional_ios_build_settings(target)
+
+    target.build_configurations.each do |config|
+      config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= [
+        '$(inherited)',
+
+        ## dart: PermissionGroup.microphone
+        'PERMISSION_MICROPHONE=1',
+      ]
+    end
   end
 end