Update as AnnotationAttribute.value is now legacyValue

Previously, this used `AnnotationAttribute.value` but that has just
been renamed to `legacyValue`.

Bug: 354633349
Test: atest check-flagged-apis-test
Change-Id: I97fdc0eadbecff10bfedaa71cabd0ae97de7fb83
diff --git a/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt b/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
index dd7c7de..25cba9c 100644
--- a/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
+++ b/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
@@ -292,7 +292,7 @@
           return item.modifiers
               .findAnnotation("android.annotation.FlaggedApi")
               ?.findAttribute("value")
-              ?.value
+              ?.legacyValue
               ?.let { Flag(it.value() as String) }
         }
       }