doom-guess-mode-h doesn't preserve text-scale

### I confirm that...

- [X] I have searched the [issue tracker](https://github.com/doomemacs/doomemacs/issues), [documentation](https://docs.doomemacs.org), [FAQ](https://docs.doomemacs.org/-/faq), [Discourse](https://discourse.doomemacs.org), and [Google](https://google.com), in case this issue has already been reported/resolved.
- [X] I have read "[How to Debug Issues](https://doomemacs.org/d/how2debug)", and will use it to provide as much information about this issue as possible.
- [X] The issue can be reproduced on the **latest** available commit of Doom.
- [X] The issue can be reproduced on a stable release of Emacs, such as 27 or 28. *(Doom does not support development builds like 29+ or any version ending in .50 or .9x)*

### Expected behavior

In a `fundamental-mode` buffer, `M-x save-buffer` doesn't have to reset text-scale.

(This issue directly mirrors #7141.)

### Current behavior

text-scale is reset on `M-x save-buffer`

### Steps to reproduce

1. Open a file `test.scrbl`
2. This should be in the `fundamental-mode` (unless you install any package that recognizes this extension--in that case switch to some other exotic extensions)
3. Make changes to the file
4. Run `M-x text-scale-increase` (perhaps via `C-x C-=` or `C-=`).
5. Run `M-x save-buffer` (perhaps via `C-x C-s` or `S-s`).

### System Information

https://pastebin.com/p7EPNSXW

Reproduce the behavior in a fundamental-mode buffer using doom-guess-mode-h, text-scale-increase, and save-buffer as described in the steps. Trace the save-buffer path and verify that the text scale remains unchanged after saving; the issue is resolved when this reproduction no longer resets text-scale.

Written by the indexing model from the issue text.