Temporal: Add test for Calendar.id with custom calendar

We already have a similar test covering TimeZone.id that ensures toString
is not called. We did not have this coverage yet for Calendar.id, so adapt
the TimeZone test for Calendar.

test/built-ins/Temporal/Calendar/prototype/id/custom-calendar.js

@@ -0,0 +1,23 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-get-temporal.calendar.prototype.id
+description: Getter does not call toString(), returns the ID from internal slot
+includes: [compareArray.js, temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const actual = [];
+const expected = [];
+
+const calendar = new Temporal.Calendar("iso8601");
+TemporalHelpers.observeProperty(actual, calendar, Symbol.toPrimitive, undefined);
+TemporalHelpers.observeProperty(actual, calendar, "toString", function () {
+  actual.push("call calendar.toString");
+  return "calendar ID";
+});
+
+const result = calendar.id;
+assert.compareArray(actual, expected);
+assert.sameValue(result, "iso8601");