Re-enable react native e2e android unit test for CI and upgrade targetSDK level for test project (#14989)
### Description
<!-- Describe your changes. -->
Re-enable the react native e2e android unit test for react native CI as
recent change of specifying `default` instead of `google-apis` in
android emulator CI tests gives pretty stable result for now.
Upgrade the targetSDKversion for gradle test project in
react-native/android to meet minimum target api level requirement for
Google Play apps.
https://support.google.com/googleplay/android-developer/answer/11926878?hl=en
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
React Native CI issue.