Update christophwurst/nextcloud requirement from ^15.0 to ^16.0

Updates the requirements on [christophwurst/nextcloud](https://github.com/ChristophWurst/nextcloud_composer) to permit the latest version.
- [Release notes](https://github.com/ChristophWurst/nextcloud_composer/releases)
- [Commits](https://github.com/ChristophWurst/nextcloud_composer/compare/v15.0.0...v16.0.2)

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

composer.json

@@ -13,7 +13,7 @@
     },
     "require-dev": {
         "roave/security-advisories": "dev-master",
-        "christophwurst/nextcloud": "^15.0",
+        "christophwurst/nextcloud": "^16.0",
         "jakub-onderka/php-parallel-lint": "^1.0.0"
     }
 }