C-o doesn't go back to agenda buffers

###

- [X] I have searched [the FAQ](https://doomemacs.org/docs/faq.org) and [the documentation](https://doomemacs.org/docs/getting_started.org) for solutions.
- [X] I have searched [the issue tracker](https://github.com/hlissner/doom-emacs/issues) for similar issues (the closed issues too).
- [X] I have searched [the Discourse](https://doomemacs.org/d/docs) for any errors and solutions.
- [X] I can reproduce my issue on [the latest commit](https://github.com/hlissner/doom-emacs/commit) of Doom Emacs.
- [X] I have read [How to Debug Issues](https://doomemacs.org/d/how2debug) and found no solution.

### What did you expect to happen?

I expect `C-o` to go back to the previous buffer, even if it's an org-agenda. But it doesn't—it takes you to a different buffer entirely. `prev-buffer` behaves the same way. There seems to be no way to go back to the agenda, apart from selecting the buffer with `SPC-<`, or generating it again with `SPC-o-A`.

### What actually happened?

`C-o` does back to *a* previous location, or buffer. But it doesn't consider the agenda to be one of these.

### Describe your attempts to resolve the issue

I don't know enough about elisp to try to fix this myself.

### Steps to reproduce

1. Open emacs
2. Open the org agenda (`SPC o A`)
3. Visit any TODO item, in that item's original file, by selecting its item and pressing RET
4. Try to go back to the agenda with `C-o`
5. Notice that you can't go back to the agenda that way

### System Information

https://pastebin.com/1Wj59X8c