Update minimum supported targetSdk to 28.

Trailing by 4 major releases, as per schedule.

Test: make
Bug: 215522897
Change-Id: I893fe0ee68cce4b08061628ed641b845d2d79b63
diff --git a/core/version_util.mk b/core/version_util.mk
index b7c4e48..b835241 100644
--- a/core/version_util.mk
+++ b/core/version_util.mk
@@ -240,6 +240,6 @@
   # Used to set minimum supported target sdk version. Apps targeting sdk
   # version lower than the set value will result in a warning being shown
   # when any activity from the app is started.
-  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 23
+  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 28
 endif
 .KATI_READONLY := PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION