fix: Fix setUTCMonth check being off by one (#2239)

Author: dcodeIO

std/assembly/date.ts

@@ -168,10 +168,10 @@ export class Date {
     this.setTime(i64(daysSinceEpoch(this.year, this.month, day)) * MILLIS_PER_DAY + ms);
   }
 
-  setUTCMonth(month: i32): void {
-    if (this.month == month) return;
+  setUTCMonth(month: i32, day: i32 = this.day): void {
+    if (this.month == month + 1) return;
     var ms = euclidRem(this.epochMillis, MILLIS_PER_DAY);
-    this.setTime(i64(daysSinceEpoch(this.year, month + 1, this.day)) * MILLIS_PER_DAY + ms);
+    this.setTime(i64(daysSinceEpoch(this.year, month + 1, day)) * MILLIS_PER_DAY + ms);
   }
 
   setUTCFullYear(year: i32): void {

std/assembly/index.d.ts

@@ -1887,7 +1887,7 @@ declare class Date {
   getUTCMilliseconds(): i32;
 
   setUTCFullYear(value: i32): void;
-  setUTCMonth(value: i32): void;
+  setUTCMonth(value: i32, day?: i32): void;
   setUTCDate(value: i32): void;
   setUTCHours(value: i32): void;
   setUTCMinutes(value: i32): void;