Use const ref instead of forwarding ref

Because we are not forwarding.

Author: joto

src/params.hpp

@@ -67,7 +67,7 @@ class params_t
         typename K, typename V,
         std::enable_if_t<!std::is_arithmetic_v<std::remove_reference_t<V>>,
                          bool> = true>
-    void set(K &&key, V &&value)
+    void set(K &&key, V const &value)
     {
         m_map.insert_or_assign(std::forward<K>(key), std::string(value));
     }