Make attribute const for enumeration getter in C++ API (#5457)

Add `const` to `attribute` in
`AttributeExperimental::get_enumeration_name`.

---
TYPE: CPP_API
DESC: Add `const` to `attribute` in
`AttributeExperimental::get_enumeration_name`

Author: jp-dark

tiledb/sm/cpp_api/attribute_experimental.h

@@ -66,7 +66,7 @@ class AttributeExperimental {
    * @return std::optional<std::string> The enumeration name if one exists.
    */
   static std::optional<std::string> get_enumeration_name(
-      const Context& ctx, Attribute& attribute) {
+      const Context& ctx, const Attribute& attribute) {
     // Get the enumeration name as a string handle
     tiledb_string_t* enmr_name;
     tiledb_ctx_t* c_ctx = ctx.ptr().get();