chore: update changes && bump app version

apps/emqx/src/emqx.app.src

@@ -2,7 +2,7 @@
 {application, emqx, [
     {id, "emqx"},
     {description, "EMQX Core"},
-    {vsn, "5.1.7"},
+    {vsn, "5.1.8"},
     {modules, []},
     {registered, []},
     {applications, [

changes/ce/fix-11424.en.md

@@ -0,0 +1 @@
+Add a check for the maximum value of the timestamp in the API to ensure it is a valid Unix timestamp.