ISBAT Issues with CoBlocks Posts block

### Describe the bug:
When a user tries to fetch content from an external feed, it results in an error on the CoBlocks Posts Block.

### To reproduce:
1. Create a new page
2. Add the Block “Posts (CoBlocks)“
3. On the right sidebar, scroll to feed settings and switch to “External Feed”.

4. Click on the “Edit RSS URL”

5. Add this feed: https://campuspress.com/feed/
6. Click on the “Use URL” Button.
7. An error similar to the one below will be displayed:

### Expected behavior:
The Block should load the posts from the given feed URL without any issues, similar to the default RSS Block.

### Isolating the problem:

- [x] This bug happens with no other plugins activated
- [x] This bug happens with a default WordPress theme active
- [x] This bug happens **without** the Gutenberg plugin active
- [x] I can reproduce this bug consistently using the steps above

### WordPress version:
6.4.3