fix: resolve CI failures from PHPStan 2 upgrade

- GcsExportAdapter: use "\n" instead of '' for empty compression option
  to preserve trailing newline in EXPORT DATA SQL
- DevBranchHandlerTest: add assertIsArray before accessing reset() result
- BigqueryTableReflectionTest: move @phpstan-ignore to own line (120 char limit)

Author: zajca

tests/Functional/Bigquery/Table/BigqueryTableReflectionTest.php

@@ -83,7 +83,8 @@ public function testColumnDefinition(
             ->dataset(self::TEST_SCHEMA)
             ->table(self::TABLE_GENERIC)
             ->info();
-        $fieldInfo = $tableInfo['schema']['fields'][1]; // @phpstan-ignore offsetAccess.nonOffsetAccessible, offsetAccess.nonOffsetAccessible
+        // @phpstan-ignore offsetAccess.nonOffsetAccessible, offsetAccess.nonOffsetAccessible
+        $fieldInfo = $tableInfo['schema']['fields'][1];
         self::assertEquals(
             RESTtoSQLDatatypeConverter::convertColumnToSQLFormat($fieldInfo), // @phpstan-ignore argument.type
             RESTtoSQLDatatypeConverter::convertColumnToSQLFormat(