Fix typo in basedocs.jl (#51334)

Thanks @DilumAluthge for finding this

Author: LilithHafner

base/docs/basedocs.jl

@@ -64,7 +64,7 @@ kw"export"
 
 `public` is used within modules to tell Julia which names are part of the
 public API of the module . For example: `public foo` indicates that the name
-`foo` is public, without making it available available when [`using`](@ref)
+`foo` is public, without making it available when [`using`](@ref)
 the module. See the [manual section about modules](@ref modules) for details.
 """
 kw"public"