Closed issue #29454 (#29475)

Changed `String` to `BitSet` as a `mutable struct` example.

(cherry picked from commit dee7d77)

doc/src/manual/calling-c-and-fortran-code.md

@@ -277,7 +277,7 @@ First, a review of some relevant Julia type terminology:
 
 | Syntax / Keyword              | Example                                     | Description                                                                                                                                                                                                                                                                    |
 |:----------------------------- |:------------------------------------------- |:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
-| `mutable struct`              | `String`                                    | "Leaf Type" :: A group of related data that includes a type-tag, is managed by the Julia GC, and is defined by object-identity. The type parameters of a leaf type must be fully defined (no `TypeVars` are allowed) in order for the instance to be constructed.              |
+| `mutable struct`              | `BitSet`                                    | "Leaf Type" :: A group of related data that includes a type-tag, is managed by the Julia GC, and is defined by object-identity. The type parameters of a leaf type must be fully defined (no `TypeVars` are allowed) in order for the instance to be constructed.              |
 | `abstract type`               | `Any`, `AbstractArray{T, N}`, `Complex{T}`  | "Super Type" :: A super-type (not a leaf-type) that cannot be instantiated, but can be used to describe a group of types.                                                                                                                                                      |
 | `T{A}`                        | `Vector{Int}`                               | "Type Parameter" :: A specialization of a type (typically used for dispatch or storage optimization).                                                                                                                                                                          |
 |                               |                                             | "TypeVar" :: The `T` in the type parameter declaration is referred to as a TypeVar (short for type variable).                                                                                                                                                                  |