🐛 Fixed incorrect autocomplete token in Setup Form (#25975)

fixes #25974

Refined the `@autocomplete` attribute in `setup.hbs` from `"username
email"` to `"email"`.

According to **WCAG Success Criterion 1.3.5 (Identify Input Purpose)**,
the autocomplete attribute must clearly and singularly define the
purpose of the input field. Using multiple tokens that do not align
strictly with the input type can confuse browsers and assistive
technologies.

---------

Co-authored-by: Steve Larson <9larsons@gmail.com>

Author: huangkevin-apr

ghost/admin/app/templates/setup.hbs

@@ -50,7 +50,7 @@
                         @name="email"
                         @placeholder="jamie@example.com"
                         @autocorrect="off"
-                        @autocomplete="username email"
+                        @autocomplete="username"
                         @value={{readonly this.email}}
                         @input={{action (mut this.email) value="target.value"}}
                         @focus-out={{action "preValidate" "email"}}

ghost/admin/app/templates/signup.hbs

@@ -39,7 +39,7 @@
                             class="gh-input"
                             placeholder="jamie@example.com"
                             autocorrect="off"
-                            autocomplete="username email"
+                            autocomplete="username"
                             value={{this.signupDetails.email}}
                             {{on "input" (fn this.setSignupProperty "email")}}
                             {{on "blur" (fn this.validate "email")}}