fix dict map! docstring: "key type"->"value type" (#34040)

Author: zsunberg

base/abstractdict.jl

@@ -710,8 +710,8 @@ end
     map!(f, values(dict::AbstractDict))
 
 Modifies `dict` by transforming each value from `val` to `f(val)`.
-Note that the type of `dict` cannot be changed: if `f(val)` is not an instance of the key type
-of `dict` then it will be converted to the key type if possible and otherwise raise an error.
+Note that the type of `dict` cannot be changed: if `f(val)` is not an instance of the value type
+of `dict` then it will be converted to the value type if possible and otherwise raise an error.
 
 # Examples
 ```jldoctest