bug#61281: “`(a \, b)” equals to “`(a . , b)”

[Xie Shynur]

In `*ielm*`:

```

ELISP> `(emacs-version \, emacs-version)

(emacs-version . "28.2")

```

________________

In `custom-file`:

```

(custom-set-variables

 '(var `(a . ,b)))

```

Then change some options by GUI menu, and click `Save Options`:

```

(custom-set-variables

 '(var `(a \, b))

 '(changed-option new-value))

```

________________

Is it a feature or bug?