Use `:orn` instead of `:altn` for map destructuring

[frenchy64]

Related https://github.com/metosin/malli/issues/1020

Map destructuring shouldn't convert to an :altn because it turns into a sequence spec when nested:

(malli.generator/generate
  [:map [:outer [:altn
                 [:map [:map [:inner :any]]]]]])
;=> {:outer [{:inner nil}]}

(m/validate
  [:map [:outer [:altn
                 [:map [:map [:inner :any]]]
                 [:seq [:* :any]]]]]
  {:outer {:inner "a"}})
;=> false

:orn is better for the job here:

(m/validate
  [:map [:outer [:orn
                 [:map [:map [:inner :any]]]
                 [:seq [:* :any]]]]]
  {:outer {:inner "a"}})
;=> true

[ikitommi]

makes sense!

[jasonjckn]

+1

[ikitommi]

Good catch, thanks!!