Polyfill: Change check to assertion in minMaxMonthLength for Hebrew calendar

This is called on dates that have already been validated, so it should be
an internal error if there is no length for a valid month code.

Author: catamorphism

polyfill/lib/calendar.mjs

@@ -1280,7 +1280,7 @@ const helperHebrew = makeNonISOHelper([{ code: 'am', isoEpoch: { year: -3760, mo
     const { month, year } = calendarDate;
     const monthCode = calendarDate.monthCode ?? this.getMonthCode(year, month);
     const daysInMonth = this.monthLengths[monthCode];
-    if (daysInMonth === undefined) throw new RangeErrorCtor(`unmatched Hebrew month: ${month}`);
+    assert(daysInMonth, 'missing daysInMonth for Hebrew month ${monthCode}`);
     return typeof daysInMonth === 'number' ? daysInMonth : daysInMonth[minOrMax];
   },
   maxLengthOfMonthCodeInAnyYear(monthCode) {