Buck: Use Android SDK 29 during build (facebook#28455)

Summary:
Fixes `test_android` and `test_docker` build failures. Thanks to dulmandakh for identifying the fix.

Changelog:
[Internal] [Android] [Changed] - Use Android SDK 29 to build during CI tests
Pull Request resolved: facebook#28455

Test Plan: Circle CI shows `test_android` and `test_docker` passing: https://app.circleci.com/jobs/github/facebook/react-native/142273

Reviewed By: sturmen

Differential Revision: D20766589

Pulled By: hramos

fbshipit-source-id: 8ef8a8ce3a6e7353ae47425accb3bd26cf1608c4

.buckconfig

@@ -1,6 +1,6 @@
 
 [android]
-  target = android-28
+  target = android-29
 
 [download]
   max_number_of_retries = 3