revert(early-init): minor simplification (not working on Emacs 28.2)

This reverts commit d5e9365.

early-init.el

@@ -36,9 +36,11 @@
 ;; set, Emacs will load the default GUI (without background alpha), and when it
 ;; is set but the value is not valid, MinEmacs will fallback to the default
 ;; alpha of 93%.
-(when-let* ((alpha (and (>= emacs-major-version 29) (getenv "MINEMACS_ALPHA")))
-            (alpha (string-to-number alpha)))
-  (push (cons 'alpha-background (if (or (zerop alpha) (> alpha 100)) 93 alpha)) default-frame-alist))
+(when (>= emacs-major-version 29)
+  (when-let* ((alpha (getenv "MINEMACS_ALPHA"))
+              (alpha (string-to-number alpha)))
+    (push (cons 'alpha-background (if (or (zerop alpha) (> alpha 100)) 93 alpha))
+          default-frame-alist)))
 
 ;; Load MinEmacs variables from the `me-vars' core module.
 (load (expand-file-name "core/me-vars.el" (file-name-directory (file-truename load-file-name))) nil t)