Target Android API Level 28

Currently, when releasing an update, we get the following warning:

Warnings

Your app currently targets API level 26 and must target at least API level 28 to ensure it is built on the latest APIs optimized for security and performance.

From August 2019, new apps must target at least Android 9.0 (API level 28).
From November 2019, app updates must target Android 9.0 (API level 28).

Tip: Change your app's target API level. Learn how.

It seems we have to target at least Android 28 starting in November, so we should do the change earlier.