Update latest.txt for 5.1.1

scripts/latest.txt

@@ -1,6 +1,6 @@
 {
-    "version": "5.1",
-    "url":     "https://docs.wagtail.org/en/stable/releases/5.1.html",
+    "version": "5.1.1",
+    "url":     "https://docs.wagtail.org/en/stable/releases/5.1.1.html",
     "minorUrl": "https://docs.wagtail.org/en/stable/releases/5.1.html",
     "lts": {
         "version": "4.1.6",