LibJS: Assert TemporalDateTimeToString if showCalendar is "never"

The only part of TemporalDateTimeToString that can fail is
MaybeFormatAnnotateCalendar which cannot fail if showCalendar is
"never" as it simply makes an empty string.
Temporal commit: tc39/proposal-temporal@a1faee6

Userland/Libraries/LibJS/Runtime/Temporal/Instant.cpp

@@ -259,8 +259,8 @@ ThrowCompletionOr<DeprecatedString> temporal_instant_to_string(VM& vm, Instant&
     // 6. Let dateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(outputTimeZone, instant, isoCalendar).
     auto* date_time = TRY(builtin_time_zone_get_plain_date_time_for(vm, output_time_zone, instant, *iso_calendar));
 
-    // 7. Let dateTimeString be ? TemporalDateTimeToString(dateTime.[[ISOYear]], dateTime.[[ISOMonth]], dateTime.[[ISODay]], dateTime.[[ISOHour]], dateTime.[[ISOMinute]], dateTime.[[ISOSecond]], dateTime.[[ISOMillisecond]], dateTime.[[ISOMicrosecond]], dateTime.[[ISONanosecond]], undefined, precision, "never").
-    auto date_time_string = TRY(temporal_date_time_to_string(vm, date_time->iso_year(), date_time->iso_month(), date_time->iso_day(), date_time->iso_hour(), date_time->iso_minute(), date_time->iso_second(), date_time->iso_millisecond(), date_time->iso_microsecond(), date_time->iso_nanosecond(), nullptr, precision, "never"sv));
+    // 7. Let dateTimeString be ! TemporalDateTimeToString(dateTime.[[ISOYear]], dateTime.[[ISOMonth]], dateTime.[[ISODay]], dateTime.[[ISOHour]], dateTime.[[ISOMinute]], dateTime.[[ISOSecond]], dateTime.[[ISOMillisecond]], dateTime.[[ISOMicrosecond]], dateTime.[[ISONanosecond]], undefined, precision, "never").
+    auto date_time_string = MUST(temporal_date_time_to_string(vm, date_time->iso_year(), date_time->iso_month(), date_time->iso_day(), date_time->iso_hour(), date_time->iso_minute(), date_time->iso_second(), date_time->iso_millisecond(), date_time->iso_microsecond(), date_time->iso_nanosecond(), nullptr, precision, "never"sv));
 
     DeprecatedString time_zone_string;
 

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp

@@ -313,8 +313,8 @@ ThrowCompletionOr<DeprecatedString> temporal_zoned_date_time_to_string(VM& vm, Z
     // 8. Let temporalDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, isoCalendar).
     auto* temporal_date_time = TRY(builtin_time_zone_get_plain_date_time_for(vm, &time_zone, *instant, *iso_calendar));
 
-    // 9. Let dateTimeString be ? TemporalDateTimeToString(temporalDateTime.[[ISOYear]], temporalDateTime.[[ISOMonth]], temporalDateTime.[[ISODay]], temporalDateTime.[[ISOHour]], temporalDateTime.[[ISOMinute]], temporalDateTime.[[ISOSecond]], temporalDateTime.[[ISOMillisecond]], temporalDateTime.[[ISOMicrosecond]], temporalDateTime.[[ISONanosecond]], isoCalendar, precision, "never").
-    auto date_time_string = TRY(temporal_date_time_to_string(vm, temporal_date_time->iso_year(), temporal_date_time->iso_month(), temporal_date_time->iso_day(), temporal_date_time->iso_hour(), temporal_date_time->iso_minute(), temporal_date_time->iso_second(), temporal_date_time->iso_millisecond(), temporal_date_time->iso_microsecond(), temporal_date_time->iso_nanosecond(), iso_calendar, precision, "never"sv));
+    // 9. Let dateTimeString be ! TemporalDateTimeToString(temporalDateTime.[[ISOYear]], temporalDateTime.[[ISOMonth]], temporalDateTime.[[ISODay]], temporalDateTime.[[ISOHour]], temporalDateTime.[[ISOMinute]], temporalDateTime.[[ISOSecond]], temporalDateTime.[[ISOMillisecond]], temporalDateTime.[[ISOMicrosecond]], temporalDateTime.[[ISONanosecond]], isoCalendar, precision, "never").
+    auto date_time_string = MUST(temporal_date_time_to_string(vm, temporal_date_time->iso_year(), temporal_date_time->iso_month(), temporal_date_time->iso_day(), temporal_date_time->iso_hour(), temporal_date_time->iso_minute(), temporal_date_time->iso_second(), temporal_date_time->iso_millisecond(), temporal_date_time->iso_microsecond(), temporal_date_time->iso_nanosecond(), iso_calendar, precision, "never"sv));
 
     DeprecatedString offset_string;