Cover endOfPeriod method of the Navigation class

The custom frequency requires a timezone configuration, forcing it
to run in the integration test scope.

Running the integration tests requires a database connection in the
build process. It enables other case tests.

The API Tests cause interference in other tests, requiring isolating
them.

tests/integration/Support/NavigationCustomEndOfPeriodTest.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Tests\integration\Support;
+
+use Carbon\Carbon;
+use FireflyIII\Support\Navigation;
+use Tests\integration\TestCase;
+
+class NavigationCustomEndOfPeriodTest extends TestCase
+{
+
+    /**
+     * @runInSeparateProcess
+     * @preserveGlobalState disabled
+     */
+    public function testGivenADateAndCustomFrequencyWhenCalculateTheDateThenReturnsTheEndOfMonthSuccessful()
+    {
+        $from       = Carbon::parse('2023-08-05');
+        $expected   = Carbon::parse('2023-09-04');
+        $navigation = new Navigation();
+
+        $period = $navigation->endOfPeriod($from, 'custom');
+        $this->assertEquals($expected->toDateString(), $period->toDateString());
+    }
+}