Fix arity error wording for a keyword

[elenam]

It looks like in Clojure 1.11 there is no longer a special case for arity exception on a keyword:

babel.middleware=> (:a 1 2 3 4)
The function :a cannot be called with four arguments.

In Clojure interactive session on line 1.
Call sequence:
[Clojure interactive session (repl)]

babel.middleware=> *e
#error {
 :cause "Wrong number of args (4) passed to: :a"
 :via
 [{:type clojure.lang.ArityException
   :message "Wrong number of args (4) passed to: :a"
   :at [clojure.lang.Keyword throwArity "Keyword.java" 108]}]

Add a special case for a function that's a keyword.

[stanislowskij]

This now corresponds to Clojure-Intro-Course/babel#58 in the migration repository.