keep the source when update post

Author: Mh-Asmi

src/Ushahidi/Modules/V5/Actions/Post/Commands/UpdatePostCommand.php

@@ -91,6 +91,7 @@ public static function fromRequest(int $id, PostRequest $request, Post $current_
             ? $request->input('base_language') : $current_post->base_language;
         $input['published_to'] = $request->has('published_to')
             ? $request->input('published_to') : $current_post->published_to;
+        $input['source'] = $current_post->source;
         $input['created'] = self::ensureTimestamp($current_post->created);
         $input['updated'] = time();