Add Luxembourgish holidays

src/Countries/Luxembourg.php

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+<?php
+
+namespace Spatie\Holidays\Countries;
+
+use Carbon\CarbonImmutable;
+
+class Luxembourg extends Country
+{
+    public function countryCode(): string
+    {
+        return 'lu';
+    }
+
+    protected function allHolidays(int $year): array
+    {
+        return array_merge([
+            'Nouvel An' => '01-01',
+            'Premier Mai' => '05-01',
+            'Journée de l\'Europe' => '05-09',
+            'Fête nationale' => '06-23',
+            'Assomption' => '08-15',
+            'Toussaint' => '11-01',
+            'Noël' => '12-25',
+            'Saint Étienne' => '12-26',
+        ], $this->variableHolidays($year));
+    }
+
+    /** @return array<string, CarbonImmutable> */
+    protected function variableHolidays(int $year): array
+    {
+        $easter = CarbonImmutable::createFromTimestamp(easter_date($year))
+            ->setTimezone('Europe/Luxembourg');
+
+        return [
+            'Lundi de Pâques' => $easter->addDay(),
+            'Ascension' => $easter->addDays(39),
+            'Lundi de Pentecôte' => $easter->addDays(50),
+        ];
+    }
+}

tests/.pest/snapshots/Countries/LuxembourgTest/it_can_calculate_luxembourgish_holidays.snap

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+[
+    {
+        "name": "Nouvel An",
+        "date": "2024-01-01"
+    },
+    {
+        "name": "Lundi de P\u00e2ques",
+        "date": "2024-04-01"
+    },
+    {
+        "name": "Premier Mai",
+        "date": "2024-05-01"
+    },
+    {
+        "name": "Ascension",
+        "date": "2024-05-09"
+    },
+    {
+        "name": "Journ\u00e9e de l'Europe",
+        "date": "2024-05-09"
+    },
+    {
+        "name": "Lundi de Pentec\u00f4te",
+        "date": "2024-05-20"
+    },
+    {
+        "name": "F\u00eate nationale",
+        "date": "2024-06-23"
+    },
+    {
+        "name": "Assomption",
+        "date": "2024-08-15"
+    },
+    {
+        "name": "Toussaint",
+        "date": "2024-11-01"
+    },
+    {
+        "name": "No\u00ebl",
+        "date": "2024-12-25"
+    },
+    {
+        "name": "Saint \u00c9tienne",
+        "date": "2024-12-26"
+    }
+]

tests/Countries/LuxembourgTest.php

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+<?php
+
+namespace Spatie\Holidays\Tests\Countries;
+
+use Carbon\CarbonImmutable;
+use Spatie\Holidays\Holidays;
+
+it('can calculate luxembourgish holidays', function () {
+    CarbonImmutable::setTestNowAndTimezone('2024-01-01');
+
+    $holidays = Holidays::for(country: 'lu')->get();
+
+    expect($holidays)
+        ->toBeArray()
+        ->not()->toBeEmpty();
+
+    expect(formatDates($holidays))->toMatchSnapshot();
+});