test: harden claim race test

crates/adapters/sqlite/tests/repositories/movie_dedup_test.rs

@@ -120,7 +120,7 @@ async fn merging_into_a_canonical_movie_that_does_not_exist_yet_succeeds() {
 }
 
 #[tokio::test]
-async fn merging_into_an_existing_canonical_movie_keeps_its_poster() {
+async fn merging_into_an_existing_canonical_movie_moves_the_external_id_and_keeps_its_poster() {
     let pool = migrated_pool().await;
     let ext = ExternalMetadataId::new("tmdb:603".into()).unwrap();
     let old_id = MovieId::generate();