M5: end-to-end test matrix and CI

- tests/integration/roundtrip.sh: key, kit code and confirmation,
  location, full and unchanged incremental backup, restore new-folder and
  replace (files identical, extra file in the trash), database dump and
  restore, retention, trash and restore from trash, no files_external
  errors in the log
- tests/integration/matrix.sh: fresh Nextcloud per version and database
  (SQLite, MariaDB, PostgreSQL), removes only its own containers and
  their volumes; locally green on NC32 and NC35 with all three databases
- GitHub Actions: unit tests on PHP 8.2-8.4, round trip on NC32-35 x
  SQLite/MariaDB/PostgreSQL

Fixes found by the matrix:
- files_external is no longer booted when it is disabled: only its
  classes are loaded and a private BackendService gets its backends from
  its Application class (booting registered its mount provider, which
  failed on installations where its tables were never created)
- SQLite: the database file is excluded from the file backup (it is
  covered by the logical dump and copying the live file is inconsistent)
- occ backup:key:confirm accepts --code and --confirm for scripts

lib/Service/BackupService.php

@@ -218,6 +218,15 @@ class BackupService {
 			'data/*/cache',
 			'data/*/uploads',
 		];
+		// SQLite: the database file is in the data directory; it is backed up by the logical dump,
+		// and copying the live file would give an inconsistent copy.
+		if ($this->config->getSystemValueString('dbtype') === 'sqlite3') {
+			$dbName = $this->config->getSystemValueString('dbname', 'owncloud');
+			$exclude[] = "data/$dbName.db";
+			$exclude[] = "data/$dbName.db-journal";
+			$exclude[] = "data/$dbName.db-wal";
+			$exclude[] = "data/$dbName.db-shm";
+		}
 		$logFile = $this->config->getSystemValueString('logfile', '');
 		if ($logFile !== '' && str_starts_with($logFile, $dataDir . '/')) {
 			$exclude[] = 'data/' . substr($logFile, strlen($dataDir) + 1);