Set auto reset for impersonate copy link button

no issue.
- updated copy link button in member impersonate modal to auto reset after clicked so that people understand they can click the button again plus it's consistent with all other task buttons

ghost/admin/app/templates/components/modal-impersonate-member.hbs

@@ -27,6 +27,7 @@
                 @value={{readonly signinUrl}}
             />
             <GhTaskButton
+                @autoReset={{true}}
                 @buttonText="Copy link"
                 @task={{this.copySigninUrl}}
                 @successText="Link copied"