release-notes: Add notes for 42.20250803.2.0 release

See: coreos/fedora-coreos-tracker#1890

Author: travier

release-notes/testing.yml

@@ -38,7 +38,9 @@ releases:
   42.20250818.2.0:
     issues: []
   42.20250803.2.0:
-    issues: []
+    issues:
+      - text: "Migrate existing systems to OCI updates"
+        url: "https://github.com/coreos/fedora-coreos-tracker/issues/1890"
   42.20250721.2.0:
     issues:
       - text: "Implement Oracle Cloud Infrastructure support"