stick to @nextcloud/files v2

* Forward ports: #5264
* Resolves: failing build in #5251

`@nextcloud/files` requires node 20 and npm 9. This dependency was introduced based on a beta version that did not have these requirements yet. Roll back to version 2 rather than updating the entire node stack.

Only difference here is that `formatFileSize` which we use will default to non-binary file sizes - i.e 1.024KB instead of 1KiB as this only became available with v3:
* https://github.com/nextcloud-libraries/nextcloud-files/pull/770/files#diff-237392127cb275fc6789cf6faec014d758950c87ccdab0329dde793d034190d8

Signed-off-by: Max <max@nextcloud.com>

package.json

@@ -39,7 +39,7 @@
     "@nextcloud/axios": "^2.4.0",
     "@nextcloud/browser-storage": "^0.3.0",
     "@nextcloud/event-bus": "^3.1.0",
-    "@nextcloud/files": "^3.0.0",
+    "@nextcloud/files": "^2.1.0",
     "@nextcloud/initial-state": "^2.1.0",
     "@nextcloud/l10n": "^2.2.0",
     "@nextcloud/logger": "^2.7.0",