test(user_ldap): speed up AbstractMappingTestCase chunking test

The testGetListOfIdsByDn test mapped a DN every 20 entries across 66k
entries, producing 3332 DB inserts just to exercise query chunking. Only
14 mapped entries are needed to exceed the 65535-value Postgres IN limit
and trigger chunking — so map every 5000th entry instead (14 inserts).

Also clarify the comment: it describes why the list exceeds Postgres's
65535-value IN limit, not a per-iteration invariant.

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

Author: miaulalala

apps/user_ldap/tests/Mapping/AbstractMappingTestCase.php

@@ -284,16 +284,16 @@ public function testGetListOfIdsByDn(): void {
 
 		$listOfDNs = [];
 		for ($i = 0; $i < 66640; $i++) {
-			// Postgres has a limit of 65535 values in a single IN list
+			// List size exceeds the implementation's 65000-parameter chunk limit, forcing multiple chunked queries
 			$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);
 	}
 }