Allow core_current to use stub-annotations

Switching from core_current to 28 allows stub-annotations to be used to
build the java libraries underpinning the core_current SDK.

Bug: 142113521
Test: m checkbuild
Change-Id: I39ce1c79cf8a0dea68c27dc38504a63a41537f51
diff --git a/Android.bp b/Android.bp
index 674343d..f56ff28 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,7 +41,8 @@
     srcs: [
         "stub-annotations/src/main/java/**/*.java",
     ],
-    sdk_version: "core_current",
+    // Allow core_current to use stub-annotations.
+    sdk_version: "28",
     target: {
         host: {
             dist: {