test(user_ldap): speed up AbstractMappingTestCase chunking test

Reduce mapped entries from 3332 to 14 (every 5000th instead of every
20th) so the test exercises the chunking path without inserting thousands
of rows. Move the explanatory comment above the loop where it belongs.

Note: the implementation chunks at its own 65000 total-parameter limit
(not Postgres's 65535 IN-list limit), so the comment uses 65000.

Signed-off-by: Anna Larch <anna@nextcloud.com>
AI-Assisted-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: miaulalala

apps/user_ldap/tests/Mapping/AbstractMappingTestCase.php

@@ -283,17 +283,17 @@ public function testGetListOfIdsByDn(): void {
 		[$mapper,] = $this->initTest();
 
 		$listOfDNs = [];
+		// List size exceeds the implementation's 65000-parameter chunk limit, forcing multiple chunked queries
 		for ($i = 0; $i < 66640; $i++) {
-			// Postgres has a limit of 65535 values in a single IN list
 			$name = 'as_' . $i;
 			$dn = 'uid=' . $name . ',dc=example,dc=org';
 			$listOfDNs[] = $dn;
-			if ($i % 20 === 0) {
+			if ($i % 5000 === 0) {
 				$mapper->map($dn, $name, 'fake-uuid-' . $i);
 			}
 		}
 
 		$result = $mapper->getListOfIdsByDn($listOfDNs);
-		$this->assertCount(66640 / 20, $result);
+		$this->assertCount(14, $result);
 	}
 }