Update phpoffice/phpspreadsheet requirement from ^2.0 to ^2.1

Updates the requirements on [phpoffice/phpspreadsheet](https://github.com/PHPOffice/PhpSpreadsheet) to permit the latest version.
- [Release notes](https://github.com/PHPOffice/PhpSpreadsheet/releases)
- [Changelog](https://github.com/PHPOffice/PhpSpreadsheet/blob/master/CHANGELOG.md)
- [Commits](PHPOffice/PhpSpreadsheet@2.0.0...2.1.0)

---
updated-dependencies:
- dependency-name: phpoffice/phpspreadsheet
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -9,7 +9,7 @@
     "php": "^8.3",
     "ext-mbstring": "*",
     "ext-pdo_sqlite": "*",
-    "phpoffice/phpspreadsheet": "^2.0",
+    "phpoffice/phpspreadsheet": "^2.1",
     "league/csv": "^9.15",
     "halaxa/json-machine": "^1.1"
   },