Don't enable Corfu in Emacs 28.1, due to strange error there

cc @minad

```
Debugger entered--Lisp error: (void-function :group)
  :group(corfu)
  byte-code("\301\302N\204\f\0\303\301\302\304#\210\303\301\305\306#\210\303\301\307\310C#\210\311\312\310\313\300!\205#\0\10\310\211%\210\314\315\316\317\320DD\321\322\323\324..." [global-corfu-mode-map global-corfu-mode-hook variable-documentation put "Hook run after entering or leaving `global-corfu-m..." custom-type hook standard-value nil add-minor-mode global-corfu-mode boundp custom-declare-variable global-corfu-modes funcall function #f(compiled-function () #<bytecode 0x1f400016fe5d4>) "Which major modes `corfu-mode' is switched on in.\n..." :type (repeat sexp) :group corfu] 9)
  global-corfu-mode()
```

lisp/init-corfu.el

@@ -14,7 +14,7 @@
       completion-category-overrides nil)
 (setq completion-cycle-threshold 4)
 
-(when (maybe-require-package 'corfu)
+(when (and (version<= "28.1" emacs-version) (maybe-require-package 'corfu))
   (setq-default corfu-auto t)
   (with-eval-after-load 'eshell
     (add-hook 'eshell-mode-hook (lambda () (setq-local corfu-auto nil))))