fix(set): clamp hour() to 23 instead of the invalid 24

hour(n) with n >= 24 clamped n to 24, which walkTo() rejects as an invalid
hour (valid range 0-23), nulling the epoch and invalidating the object.
Clamp to 23 to match the other overflow-clamping setters (date, month).

src/methods/set/set.js

@@ -67,8 +67,10 @@ const minutes = function (s, n, goFwd) {
 
 const hours = function (s, n, goFwd) {
   n = validate(n)
+  // clamp to a valid hour (0-23). Clamping to 24 produces an hour that
+  // walkTo() rejects, which nulls the epoch and invalidates the object.
   if (n >= 24) {
-    n = 24
+    n = 23
   } else if (n < 0) {
     n = 0
   }