fix(comments): Fix activity rich subject parameters

Signed-off-by: provokateurin <kate@provokateurin.de>

apps/comments/lib/Activity/Provider.php

@@ -174,10 +174,13 @@ class Provider implements IProvider {
 		}
 	}
 
+	/**
+	 * @return array<string, string>
+	 */
 	protected function generateFileParameter(int $id, string $path): array {
 		return [
 			'type' => 'file',
-			'id' => $id,
+			'id' => (string)$id,
 			'name' => basename($path),
 			'path' => $path,
 			'link' => $this->url->linkToRouteAbsolute('files.viewcontroller.showFile', ['fileid' => $id]),