Fix graph bug when hovering over last value

src/lib/components/test_cases/TestCaseGraph.svelte

@@ -1276,9 +1276,9 @@
                                         class="self-end mt-0.5 ml-1 text-nowrap text-sm text-gray-800 bg-gray-200 px-1.5 rounded-lg"
                                       >
                                         {@html formatLongOrdinalSup(
-                                          deciles.find(
+                                          (deciles.find(
                                             ([, end]) => end > delta[index],
-                                          )[0],
+                                          ) ?? deciles[deciles.length - 1])[0],
                                         )} dixième
                                       </span>
                                     {/if}