transient-information: Use a space as the fake key

Most suffix bindings are one character long.  The default `format'
for both proper suffixes and display-only suffixes is " %k %d".
Therefore, if we use something that is one character long as the
face key, then things are aligned most of the time.

lisp/transient.el

@@ -753,7 +753,8 @@ slot is non-nil."
   "Superclass for suffix command.")
 
 (defclass transient-information (transient-suffix)
-  ((format :initform " %k %d"))
+  ((format :initform " %k %d")
+   (key    :initform " "))
   "Display-only information.
 A suffix object with no associated command.")