Temporal: Add a test for a coverage gap in Duration.prototype.round

See https://github.com/tc39/proposal-temporal/issues/2919; this adds test
coverage that would have caught an unintentional normative change.

test/built-ins/Temporal/Duration/prototype/round/end-of-month-round-up.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.round
+description: Correctly handle special case where rounding value is at upper bound
+info: |
+  sec-temporal-nudgetocalendarunit:
+    1. If _progress_ = 1, then
+      1. Let _roundedUnit_ be abs(_r2_).
+    1. Else,
+      1. Let _roundedUnit_ be ApplyUnsignedRoundingMode(abs(_total_), abs(_r1_),
+         abs(_r2_), _unsignedRoundingMode_).
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const instance = new Temporal.Duration(0, 11);
+const relativeTo = new Temporal.PlainDate(2023, 5, 31);
+const result = instance.round({ relativeTo, smallestUnit: "months", roundingMode: "ceil" });
+TemporalHelpers.assertDuration(result, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0);